media: vidtv: extract the initial CRC value to into a #define

The same constant (0xffffffff) is used in three different functions.

Extract it into a #define to avoid repetition.

Signed-off-by: Daniel W. S. Almeida <dwlsalmeida@gmail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>