platform/x86/amd/pmf: Use memdup_user()

Switch to memdup_user() to overwrite the allocated memory only once
instead of initializing the allocated memory to zero with kzalloc() and
then immediately overwriting it with copy_from_user().

Fixes the following Coccinelle/coccicheck warning reported by
memdup_user.cocci:

	WARNING opportunity for memdup_user
Signed-off-by: Thorsten Blum <thorsten.blum@toblux.com>
Link: https://lore.kernel.org/r/20240527083628.210491-2-thorsten.blum@toblux.comReviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>

drivers/platform/x86/amd/pmf/tee-if.c

@@ -301,14 +301,9 @@ static ssize_t amd_pmf_get_pb_data(struct file *filp, const char __user *buf,
 		return -EINVAL;
 
 	/* re-alloc to the new buffer length of the policy binary */
-	new_policy_buf = kzalloc(length, GFP_KERNEL);
-	if (!new_policy_buf)
-		return -ENOMEM;
-
-	if (copy_from_user(new_policy_buf, buf, length)) {
-		kfree(new_policy_buf);
-		return -EFAULT;
-	}
+	new_policy_buf = memdup_user(buf, length);
+	if (IS_ERR(new_policy_buf))
+		return PTR_ERR(new_policy_buf);
 
 	kfree(dev->policy_buf);
 	dev->policy_buf = new_policy_buf;