media: si2165: Make checkpatch happy

Fix almost all of checkpatch --strict warnings.

The remaining warnings are about:
* macro REG16 (should be enclosed in parentheses)
* macro REG16 (Macro argument reuse)

Signed-off-by: Matthias Schwarzott <zzam@gentoo.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>