media: v4l2-ctrls.h: fix v4l2_ctrl field description typos

Signed-off-by: Baruch Siach <baruch@tkos.co.il>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>