V4L/DVB (13829): uvcvideo: Fix alternate setting selection in isochronous mode

Unlike assumed by the driver, alternate settings are not sorted by
endpoint max packet size. Iterate over all alternate settings to find
the one with the smallest compatible max packet size.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>