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

Since commit 481b960, 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>

drivers/net/wireless/rtlwifi/Kconfig

@@ -50,7 +50,7 @@ config RTLWIFI
 	default m
 
 config RTLWIFI_DEBUG
-	tristate "Additional debugging output"
+	bool "Additional debugging output"
 	depends on RTL8192CE || RTL8192CU || RTL8192SE || RTL8192DE
 	default y