xfs: remove the expr argument to XFS_TEST_ERROR

Don't pass expr to XFS_TEST_ERROR.  Most calls pass a constant false,
and the places that do pass an expression become cleaner by moving it
out.

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