[media] uvcvideo: Support allocating buffers larger than the current frame size

The queue_setup handler takes an optional format argument that can be
used to allocate buffers for a format different than the current format.
The uvcvideo driver doesn't support changing the format when buffers
have been allocated, but there's no reason not to support allocating
buffers larger than the minimum size.

When the format argument isn't NULL verify that the requested image size
is large enough for the current format and use it for the buffer size.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Tested-by: Philipp Zabel <p.zabel@pengutronix.de>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>