[media] tlg2300: fix up check_firmware() return

The caller doesn't check the return value of check_firmware() but static
checkers complain.  It currently returns negative error codes, or zero
or greater on success but since the return type is boolean the values
are truncated to one or zero.  I've changed it to return an int,
negative on error and zero on success.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>