xfs: rearrange xfs_btree_cur fields for better packing

Reduce the size of the btree cursor structure some more by rearranging
fields to eliminate unused space.  While we're at it, fix the ragged
indentation and a spelling error.

Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Dave Chinner <dchinner@redhat.com>