[media] rtl2832: fix compiler warning

[media] rtl2832: fix compiler warning

>From the daily build:

rtl2832.c: In function 'rtl2832_read_status':
rtl2832.c:703:12: warning: 'tmp' may be used uninitialized in this function [-Wmaybe-uninitialized]
  } else if (tmp == 10) {
            ^

The code is OK, it's just the compiler that cannot figure out what's
going on. So just init 'tmp' to 0.

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>