[media] si2165: Refactoring for si2165_writereg_mask8()

[media] si2165: Refactoring for si2165_writereg_mask8()

This issue was detected by using the Coccinelle software.

1. Let us return directly if a call of the si2165_readreg8()
   function failed.

2. Reduce the scope for the local variables "ret" and "tmp" to one branch
   of an if statement.

3. Delete the jump label "err" then.

4. Return the value from a call of the si2165_writereg8() function
   without using an extra assignment for the variable "ret" at the end.

Signed-off-by: Markus Elfring <elfring@users.sourceforge.net>
Signed-off-by: Matthias Schwarzott <zzam@gentoo.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>