media: i2c: st-vgxy61: Convert to CCI register access helpers

Use the new common CCI register access helpers to replace the private
register access helpers in the st-vgxy61 driver. This simplifies the
driver by reducing the amount of code.

st-vgxy61 devices use little endianness arrangement, therefore
the driver uses the CCI_REGx_LE registers definition.

Signed-off-by: Julien Massot <julien.massot@collabora.com>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>