media: docs: selection: fix typos

Fix typos in the selection documentation:
 - over -> cover
 - BONDS -> BOUNDS

Signed-off-by: Luca Ceresoli <luca@lucaceresoli.net>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>