xfs: standardize the btree maxrecs function parameters

xfs: standardize the btree maxrecs function parameters

Source kernel commit: 411a71256de6f5a0015a28929cfbe6bc36c503dc

Standardize the parameters in xfs_{alloc,bm,ino,rmap,refcount}bt_maxrecs
so that we have consistent calling conventions.  This doesn't affect the
kernel that much, but enables us to clean up userspace a bit.

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