xfs: xfs_btree_staging.h: delete duplicated words

Drop the repeated words "with" and "be" in comments.

Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Cc: "Darrick J. Wong" <darrick.wong@oracle.com>
Cc: linux-xfs@vger.kernel.org
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>