media: siano: be sure to not override devpath size

Right now, at siano driver, all places where devpath is
defined has sizeof(devpath) == 32. So, there's no practical
risc of going past devpath array anywhere.

Still, code changes might cause troubles. It also confuses
Coverity:
	CID 139059 (#1 of 1): Copy into fixed size buffer (STRING_OVERFLOW)
	9. fixed_size_dest: You might overrun the 32-character
	   fixed-size string entry->devpath by copying devpath
	   without checking the length.
	10. parameter_as_source: Note: This defect has an
	    elevated risk because the source argument
	    is a parameter of the current function.

So, explicitly limit strcmp() and strcpy() to ensure that the
devpath size (32) will be respected.

Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>