media: i2c: adv7842: convert to i2c_new_dummy_device

Move away from the to-be-removed i2c_new_dummy() to
i2c_new_dummy_device(). So, we now get an ERRPTR which we use in error
handling by printing the error code. To keep the rest of the driver
logic as is, internally a NULL ptr is still kept.

Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>