media: ov2640: make s_ctrl() work in power-down mode

The s_ctrl() operation can be called when the device is placed into
power down mode.  Then, applying controls to H/W should be postponed at
this time.  Instead the controls will be restored when the streaming is
started.

Cc: Mauro Carvalho Chehab <mchehab@s-opensource.com>
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>