xfs: stricter btree height checking when looking for errors

Since each btree type has its own precomputed maxlevels variable now,
use them instead of the generic XFS_BTREE_MAXLEVELS to check the level
of each per-AG btree.

Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Chandan Babu R <chandan.babu@oracle.com>