[media] cx25821: Remove bad strcpy to read-only char*

The strcpy was being used to set the name of the board.
This was both wrong and redundant,
since the destination char* was read-only and
the name is set statically at compile time.

The type of the name field is changed to const char*
to prevent future errors.

Reported-by: Radek Masin <radek@masin.eu>
Signed-off-by: Ezequiel Garcia <elezegarcia@gmail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>