xfs: ensure committed is initialized in xfs_trans_roll

__xfs_trans_roll() can return without setting the
*committed argument; this was a problem for xfs_bmap_finish():

        int       committed;/* xact committed or not */
...
        error = __xfs_trans_roll(tp, ip, &committed);
        if (error) {
...
                if (committed) {

and we tested an uninitialized "committed" variable on the
error path.  No caller is preserving "committed" state across
calls to __xfs_trans_roll(), so just initialize committed inside
the function to avoid future errors like this.
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Eric Sandeen <sandeen@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Dave Chinner <david@fromorbit.com>

fs/xfs/xfs_trans.c

@@ -1028,6 +1028,8 @@ __xfs_trans_roll(
 	struct xfs_trans_res	tres;
 	int			error;
 
+	*committed = 0;
+
 	/*
 	 * Ensure that the inode is always logged.
 	 */
@@ -1082,6 +1084,6 @@ xfs_trans_roll(
 	struct xfs_trans	**tpp,
 	struct xfs_inode	*dp)
 {
-	int			committed = 0;
+	int			committed;
 	return __xfs_trans_roll(tpp, dp, &committed);
 }