dlm: Fix uninitialised variable warning in lock.c

  CC [M]  fs/dlm/lock.o
fs/dlm/lock.c: In function ‘find_rsb’:
fs/dlm/lock.c:438: warning: ‘r’ may be used uninitialized in this function

Since r is used on the error path to set r_ret, set it to NULL.
Signed-off-by: Steven Whitehouse <swhiteho@redhat.com>
Signed-off-by: David Teigland <teigland@redhat.com>

fs/dlm/lock.c

@@ -435,7 +435,7 @@ static int search_rsb(struct dlm_ls *ls, char *name, int len, int b,
 static int find_rsb(struct dlm_ls *ls, char *name, int namelen,
 		    unsigned int flags, struct dlm_rsb **r_ret)
 {
-	struct dlm_rsb *r, *tmp;
+	struct dlm_rsb *r = NULL, *tmp;
 	uint32_t hash, bucket;
 	int error = -EINVAL;