[media] drxk: remove _0 from read/write routines

The normal 16-bits read routine is called as "Read16_0". This is
due to a flags that could optionally be passed. Yet, on no places
at the code, a flag is passed there.

The same happens with 16-bits write and 32-read/write routines,
and with WriteBlock.

Also, using flags, is an exception: there's no place currently using
flags, except for an #ifdef at WriteBlock.

Rename the function as just "read16", and the one that requires flags,
as "read16_flags".

This helps to see where the flags are used, and also avoid using
CamelCase on Kernel.
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>