media: mt9m001: introduce multi_reg_write()

Introduce multi_reg_write() to write multiple registers to the device and
use it where possible.

Cc: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
Signed-off-by: Akinobu Mita <akinobu.mita@gmail.com>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>