xfs: avoid nested calls to __xfs_trans_commit

Currently, __xfs_trans_commit calls xfs_defer_finish_noroll, which calls
__xfs_trans_commit again on the same transaction.  In other words,
there's a nested function call (albeit with slightly different
arguments) that has caused minor amounts of confusion in the past.
There's no reason to keep this around, since there's only one place
where we actually want the xfs_defer_finish_noroll, and that is in the
top level xfs_trans_commit call.

This also reduces stack usage a little bit.

Signed-off-by: "Darrick J. Wong" <djwong@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>