media: ov08x40: Improve ov08x40_[read|write]_reg() error returns

Improve ov08x40_[read|write]_reg() error returns, if we got an errno value
from the I2C core use that instead of always returning -EIO.

Tested-by: Bryan O'Donoghue <bryan.odonoghue@linaro.org>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>