media: adv7180: Remove duplicate checks

Since i2c_unregister_device() became NULL-aware we may remove duplicate checks.

Cc: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>