xfs: fix number of records handling in xfs_iext_split_leaf

xfs: fix number of records handling in xfs_iext_split_leaf

Source kernel commit: 43d193aa0212691254d574b8d207609ef22018b8

Fix to check the correct value, and remove a duplicate handling of the
uneven record number split algorith,

Reported-by: Brian Foster <bfoster@redhat.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Brian Foster <bfoster@redhat.com>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Eric Sandeen <sandeen@sandeen.net>