V4L/DVB (9453): stb0899: fix compilation warnings

Cleanup/Optimization:
* Fix compile warnings
* The compile warnings helped to identify 2 unnecessary I/O operations

Signed-off-by: Manu Abraham <manu@linuxtv.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>