rtlwifi: Fix breakage in debug functions when built as a module

Since commit 481b9606, it has not been possible to invoke debugging
with any rtlwifi driver built as a module.

Reported-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: Larry Finger <Larry.Finger@lwfinger.net>
Cc: Joe Perches <joe@perches.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>