grabbers: v4l2: Fail on unsupported pixel format
grabbers: v4l2: Fail on unsupported pixel format

We only requst the pixel format, if the request cannot be granted we will
get different than we had requested.

So we should check the resulting pixel format and abort if we got
unexpeceted one.

Signed-off-by: Cyril Hrubis <b1e90efd3b808b8e0bcf2a9a55fd8b9a779bfd81@ucw.cz>

gfxprim/gfxprim,gfxprim/gfxprim,gfxprim/gfxprim,gfxprim/gfxprim,gfxprim/gfxprim