[media] V4L: ov9740: Correct print in ov9740_reg_rmw()

The register width of the ov9740 is 16-bits, so correct the debug print
to reflect this.

Signed-off-by: Andrew Chew <achew@nvidia.com>
Signed-off-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>