media: ov7670: do not aggregate returns

Adding muliple status together loses individual failures.
Check each status separately.

Clean up some other returns for consistency.

Fixed several coding style problems by running
the file through checkpatch.pl --fix-inplace

Signed-off-by: Tom Rix <trix@redhat.com>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>