xfs: rename code to error in xfs_ioctl_setattr

Rename the 'code' variable to 'error' to follow the naming convention of
most other functions in xfs.

Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Chaitanya Kulkarni <chaitanya.kulkarni@wdc.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Brian Foster <bfoster@redhat.com>