[media] V4L: sh_mobile_ceu_camera: fix typos in documentation

Fix a couple of typos and clarify a formula in sh_mobile_ceu driver
documentation.

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