media: i2c: ov9281: Remove override of subdev name

From the original Rockchip driver, the subdev was renamed
from the default to being "mov9281 <dev_name>" whereas the
default would have been "ov9281 <dev_name>".

Remove the override to drop back to the default rather than
a vendor custom string.

Signed-off-by: Dave Stevenson <dave.stevenson@raspberrypi.com>