GFS2: Fix infinite loop in rbm_find

This patch fixes an infinite loop in gfs2_rbm_find that was introduced
by the previous patch. The problem occurred when the length was less
than 3 but the rbm block was byte-aligned, causing it to improperly
return a extent length of zero, which caused it to spin.

Signed-off-by: Bob Peterson <rpeterso@redhat.com>
Signed-off-by: Steven Whitehouse <swhiteho@redhat.com>
Tested-by: Bob Peterson <rpeterso@redhat.com>
Tested-by: Barry Marson <bmarson@redhat.com>

fs/gfs2/rgrp.c

@@ -329,6 +329,7 @@ static u32 gfs2_free_extlen(const struct gfs2_rbm *rrbm, u32 len)
 	    gfs2_unaligned_extlen(&rbm, 4 - n_unaligned, &len))
 		goto out;
 
+	n_unaligned = len & 3;
 	/* Start is now byte aligned */
 	while (len > 3) {
 		start = rbm.bi->bi_bh->b_data;