[media] gspca: store current mode instead of individual parameters

Store complete current mode (struct v4l2_pix_format) in struct gspca_dev
instead of separate pixfmt, width and height parameters.
This is a preparation for variable resolution support.

Signed-off-by: Ondrej Zary <linux@rainbow-software.org>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>