[media] media: ov6650: stylistic improvements

* with no "retrun ret;" at the end, there is no need to initialize ret
  any longer,
* consequently use conditional expressions, not if...else constructs,
  throughout ov6650_s_ctrl(),
* v4l2_ctrl_new_std_menu() max value of V4L2_EXPOSURE_MANUAL instead of
  equivalent 1 looks more clear.

Created on top of "Converting soc_camera to the control framework"
series.

Signed-off-by: Janusz Krzysztofik <jkrzyszt@tis.icnet.pl>
Signed-off-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>