V4L/DVB (5888): zr36067: Driver was not returning correct image size

The driver was returning the size of the (fixed) buffer it allocated as the
sizeimage field in the v4l2 pixel format, rather than the actual size of the
image.  For example, a 192x128 YUYV image is 49152 bytes but the driver would
always return 131072 bytes since if that was the size of the v4l buffer.

This violates the v4l2 spec, which says that sizeimage should be the actual
size of the image for uncompressed formats.  It also caused mplayer to crash.

Signed-off-by: Trent Piepho <xyzzy@speakeasy.org>
Acked-by: Ronald S. Bultje <rbultje@ronald.bitfreak.net>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>