V4L/DVB (8158): gspca: minor changes

main: V4L2_PIX_FMT_SPCA501 is compressed (thanks to Hans de Goede)
main: return 0 when no change on vidioc_s_fmt_cap (thanks to Hans de Goede)
pac207: cleanup

Signed-off-by: Jean-Francois Moine <moinejf@free.fr>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>