V4L/DVB (9788): soc-camera: simplify naming

We anyway don't follow the s_fmt_vid_cap / g_fmt_vid_cap / try_fmt_vid_cap
naming, and soc-camera is so far only about video capture, let's simplify
operation names a bit further. set_fmt_cap / try_fmt_cap wasn't a very good
choice too.

Signed-off-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>