V4L/DVB (12853): tm6000: Fix almost all warnings at the driver

Onr warning is left, since it is there for a purpose:
tm6000-core.c:218: warning: ISO C90 forbids mixed declarations and code

It indicates a place where a temporary hack were added. Tests are needed to be sure that
we can remove it.

Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>