V4L/DVB (10283): cx18: Call request_module() with proper argument types.

request_module() needs to be called with a string literal for a
format string or with 1 or more variable arguments to avoid
compiler warnings and possible exploits, if someone could cause
us to get a format string with a '%' code in the format string
when we make the call.

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