V4L/DVB (13242): gspca_mr97310a: Add minimum clock divider control

When "shooting" certain (quite rare) scenes, the mr97310's compression is not
effective and it cannot keep up with the data stream. This patch adds a
minimum clock divider control, which influences the maximum framerate,
libv4l will automatically increase this minimum clockdiv control when it
detect the cam cannot keep up.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>