media: dt-bindings: media: mt9m111: add pclk-sample property

Add the pclk-sample property to the list of optional properties
for the mt9m111 camera sensor.

Signed-off-by: Marco Felsch <m.felsch@pengutronix.de>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>