media: mt9p031: Increase post-reset delay

The MT9P006 sensor driver sporadically fails to probe because the sensor
responds with a NACK condition to I2C address on the bus during an attempt
to read the sensor MT9P031_CHIP_VERSION register in mt9p031_registered().

Neither the MT9P006 nor MT9P031 datasheets are clear on reset signal timing.
Older MT9M034 [1] datasheet provides those timing figures in Appendix-A and
indicates it is necessary to wait 850000 EXTCLK cycles before starting any
I2C communication.

Add such a delay, which does make the sporadic I2C NACK go away, so it is
likely similar constraint applies to this sensor.

[1] https://www.onsemi.com/pdf/datasheet/mt9m034-d.pdf



Signed-off-by: Marek Vasut <marex@denx.de>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>