media: i2c: ov5640: Fix post-reset delay

According to the ov5640 specification (2.7 power up sequence), host can
access the sensor's registers 20ms after reset. Trying to access them
before leads to undefined behavior and result in sporadic initialization
errors.

Signed-off-by: Loic Poulain <loic.poulain@linaro.org>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>