rtlwifi: Let rtlwifi build when PCI is not enabled

On systems where PCI does not exist, a build of rtlwifi will fail.
Apply the same fix in case there are systems with PCI but not USB.

Signed-off-by: Willy Tarreau <w@1wt.eu>
Signed-off-by: Larry Finger <Larry.Finger@lwfinger.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>