V4L/DVB (8915): cx18: Increment u8 pointers not void pointers.

cx18: Increment u8 pointers not void pointers.  Incrementing void pointers
is dubious and the real intent in cx18_memcpy_fromio() and cx18_memset_io() is
to increment by bytes, so use u8 pointers instead.

Signed-off-by: Andy Walls <awalls@radix.net>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>