media: ov5647: Rationalize driver structure name

The driver structure name is referred to with different names ('ov5647',
'state', 'sensor') in different functions in the driver.

Polish this up by using 'struct ov5647 *sensor' everywhere.

Signed-off-by: Jacopo Mondi <jacopo@jmondi.org>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>