To generate the patch for the CWE-476 (NULL Pointer Dereference) vulnerability at line 72, we need to follow a structured approach to identify the root cause and then apply a suitable fix. Here are the reasoning steps:

### Step 1: Root Cause Analysis

1. **Understanding the Code Context:**
   - The function `mv643xx_eth_shared_probe` is responsible for probing a platform device.
   - The variable `pd` is assigned the platform data from the device `pdev` at line 4.
   - The variable `msp` is allocated memory using `kzalloc` at line 21.
   - The code checks if `pd` or `pd->shared_smi` is `NULL` at line 31.
   - The variable `msp` is being initialized with various values, including `msp->tx_csum_limit` at line 72.

2. **Identifying the Vulnerability:**
   - At line 72, the code attempts to assign a value to `msp->tx_csum_limit` using the ternary operator.
   - The expression `pd->tx_csum_limit ? pd->tx_csum_limit : 9 * 1024` assumes that `pd` is not `NULL`.
   - If `pd` is `NULL`, dereferencing `pd->tx_csum_limit` will result in a NULL pointer dereference, leading to a crash or undefined behavior.

3. **Conditions Leading to Vulnerability:**
   - The check at line 31 ensures that `pd` is not `NULL` at that point in the code.
   - However, there is no guarantee that `pd` remains non-NULL throughout the function, especially at line 72.
   - Therefore, a direct dereference of `pd` without checking if it is `NULL` is unsafe.

### Step 2: Fixing Strategy

1. **Ensuring Safety:**
   - To prevent the NULL pointer dereference, we need to ensure that `pd` is not `NULL` before accessing `pd->tx_csum_limit`.
   - This can be achieved by adding a NULL check for `pd` in the ternary operator.

2. **Applying the Fix:**
   - Modify the line to include a check for `pd` being non-NULL before accessing `pd->tx_csum_limit`.
   - The corrected line should be:
     ```c
     msp->tx_csum_limit = (pd != NULL && pd->tx_csum_limit) ? pd->tx_csum_limit : 9 * 1024;
     ```

### Conclusion

The patch ensures that `pd` is checked for NULL before accessing `pd->tx_csum_limit`, thereby preventing a potential NULL pointer dereference. The reasoning steps for generating this patch are as follows:

1. **Identify the Vulnerability:**
   - Recognize that dereferencing `pd->tx_csum_limit` without checking if `pd` is `NULL` can lead to a NULL pointer dereference.

2. **Determine the Fix:**
   - Add a NULL check for `pd` in the ternary operator to ensure safe access to `pd->tx_csum_limit`.

3. **Apply the Patch:**
   - Modify the code to:
     ```c
     msp->tx_csum_limit = (pd != NULL && pd->tx_csum_limit) ? pd->tx_csum_limit : 9 * 1024;
     ```

This patch ensures that the code safely handles the case where `pd` might be `NULL`, thus preventing the CWE-476 vulnerability.