rtlwifi: Remove extern from function prototypes

There are a mix of function prototypes with and without extern
in the kernel sources.  Standardize on not using extern for
function prototypes.

Function prototypes don't need to be written with extern.
extern is assumed by the compiler.  Its use is as unnecessary as
using auto to declare automatic/local variables in a block.

Signed-off-by: Joe Perches <joe@perches.com>

drivers/net/wireless/rtlwifi/rtl8192cu/rf.h

@@ -34,15 +34,14 @@
 #define RF6052_MAX_REG			0x3F
 #define RF6052_MAX_PATH			2
 
-extern void rtl92cu_phy_rf6052_set_bandwidth(struct ieee80211_hw *hw,
-					    u8 bandwidth);
-extern void rtl92c_phy_rf6052_set_cck_txpower(struct ieee80211_hw *hw,
-					      u8 *ppowerlevel);
-extern void rtl92c_phy_rf6052_set_ofdm_txpower(struct ieee80211_hw *hw,
-					       u8 *ppowerlevel, u8 channel);
+void rtl92cu_phy_rf6052_set_bandwidth(struct ieee80211_hw *hw, u8 bandwidth);
+void rtl92c_phy_rf6052_set_cck_txpower(struct ieee80211_hw *hw,
+				       u8 *ppowerlevel);
+void rtl92c_phy_rf6052_set_ofdm_txpower(struct ieee80211_hw *hw,
+					u8 *ppowerlevel, u8 channel);
 bool rtl92cu_phy_rf6052_config(struct ieee80211_hw *hw);
 bool rtl92cu_phy_config_rf_with_headerfile(struct ieee80211_hw *hw,
-					  enum radio_path rfpath);
+					   enum radio_path rfpath);
 void rtl92cu_phy_rf6052_set_cck_txpower(struct ieee80211_hw *hw,
 					u8 *ppowerlevel);
 void rtl92cu_phy_rf6052_set_ofdm_txpower(struct ieee80211_hw *hw,