Most x86/ACPI boards use the ov2680 with a 19.2 MHz xvclk,
rather then the expected 24MHz, add support for this.

Compensate for the lower clk by setting a higher PLL multiplier
of 69 when using 19.2 MHz vs the default multiplier of 55 for
a 24MHz xvclk.
Acked-by: Rui Miguel Silva <rmfrfs@gmail.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>