media: usbtv: Use V4L2 defines to select capture resolution

Make use of the V4L2_STD_525_60 and V4L2_STD_625_50 defines to
determine the vertical resolution to use when capturing.

V4L2_STD_525_60 (resp. V4L2_STD_625_50) is the set of standards using
525 (resp. 625) lines per frame, independently of the color encoding.

Signed-off-by: Hugo Grostabussiat <bonstra@bonstra.fr.eu.org>
Signed-off-by: Hans Verkuil <hansverk@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>