Thank you for providing the code and identifying the vulnerability. The vulnerability in line 28 is related to CWE-476 (NULL Pointer Dereference). Here are five possible patches to address this vulnerability:

Patch 1: Early return with error code
```
27         propname = kasprintf(GFP_KERNEL, "pinctrl-%d", state);
28         if (!propname) {
29             of_node_put(np);
30             return -ENOMEM;
31         }
```

Patch 2: Use a goto statement to handle the error
```
27         propname = kasprintf(GFP_KERNEL, "pinctrl-%d", state);
28         if (!propname) {
29             ret = -ENOMEM;
30             goto err;
31         }
```

Patch 3: Use a temporary variable and check before assignment
```
27         char *temp_propname = kasprintf(GFP_KERNEL, "pinctrl-%d", state);
28         if (!temp_propname) {
29             of_node_put(np);
30             return -ENOMEM;
31         }
32         propname = temp_propname;
```

Patch 4: Use a default value if allocation fails
```
27         propname = kasprintf(GFP_KERNEL, "pinctrl-%d", state);
28         if (!propname) {
29             propname = "pinctrl-default";
30             dev_warn(p->dev, "Failed to allocate memory for propname, using default\n");
31         }
```

Patch 5: Implement a retry mechanism
```
27         int retry_count = 3;
28         do {
29             propname = kasprintf(GFP_KERNEL, "pinctrl-%d", state);
30             if (propname)
31                 break;
32             retry_count--;
33             msleep(10);
34         } while (retry_count > 0);
35         if (!propname) {
36             of_node_put(np);
37             return -ENOMEM;
38         }
```

These patches aim to handle the case where memory allocation fails and prevent potential NULL pointer dereference. Each patch has its own approach to addressing the issue, and the choice of which to use would depend on the specific requirements and constraints of your project.