AFS: Potential null dereference

It seems clear from the surrounding code that xpermits is allowed to be
NULL here.

Signed-off-by: Dan Carpenter <error27@gmail.com>
Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/fs/afs/security.c b/fs/afs/security.c
index 3ef5043..bb4ed14 100644
--- a/fs/afs/security.c
+++ b/fs/afs/security.c
@@ -189,8 +189,9 @@
 	if (!permits)
 		goto out_unlock;
 
-	memcpy(permits->permits, xpermits->permits,
-	       count * sizeof(struct afs_permit));
+	if (xpermits)
+		memcpy(permits->permits, xpermits->permits,
+			count * sizeof(struct afs_permit));
 
 	_debug("key %x access %x",
 	       key_serial(key), vnode->status.caller_access);