media: v4l2-common: get rid of struct v4l2_discrete_probe

This struct is there just two store two arguments of
v4l2_find_nearest_format(). The other two arguments are passed
as parameter.

IMHO, there isn't much sense on doing that, and that will just
add one more struct to document ;)

So, let's get rid of the struct, passing the parameters directly.

Acked-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Acked-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>