media: ov5647: Program mode at s_stream(1) time

Rename __sensor_init() function to ov5647_set_mode() as the function
is a regular one and the double underscores prefix shall be removed, and
then move it to program the mode at s_stream(1) time, not at sensor power
up.

Break out from __sensor_init() the stream_off() operation call at sensor
power up to coax the lanes in LP-11 state.

Signed-off-by: Jacopo Mondi <jacopo@jmondi.org>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>