jfs: Add missing mutex_unlock call to error path

Jan Kucera found an missing call to mutex_unlock() with his static code
checker.  It's an unlikely error path to hit in the real world, but it
should be fixed.
Signed-off-by: Dave Kleikamp <shaggy@linux.vnet.ibm.com>
Reported-by: Jan Kucera <kucera.jan.cz@gmail.com>

fs/jfs/jfs_imap.c

@@ -2571,6 +2571,7 @@ diNewIAG(struct inomap * imap, int *iagnop, int agno, struct metapage ** mpp)
 
 			txAbort(tid, 0);
 			txEnd(tid);
+			mutex_unlock(&JFS_IP(ipimap)->commit_mutex);
 
 			/* release the inode map lock */
 			IWRITE_UNLOCK(ipimap);