xfs: gut error handling in xfs_trans_unreserve_and_mod_sb()

commit dc3ffbb1 upstream.

The error handling in xfs_trans_unreserve_and_mod_sb() is largely
incorrect - rolling back the changes in the transaction if only one
counter underruns makes all the other counters incorrect. We still
allow the change to proceed and committing the transaction, except
now we have multiple incorrect counters instead of a single
underflow.

Further, we don't actually report the error to the caller, so this
is completely silent except on debug kernels that will assert on
failure before we even get to the rollback code.  Hence this error
handling is broken, untested, and largely unnecessary complexity.

Just remove it.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Acked-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Chandan Babu R <chandan.babu@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>