rtw89: remove unneeded variable

Fix the following coccicheck review:
./drivers/net/wireless/realtek/rtw89/mac.c: 1096: 5-8: Unneeded variable

Remove unneeded variable used to store return value.
Reported-by: Zeal Robot <zealci@zte.com.cn>
Signed-off-by: Changcheng Deng <deng.changcheng@zte.com.cn>
Acked-by: Ping-Ke Shih <pkshih@realtek.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20211110121135.151187-1-deng.changcheng@zte.com.cn

drivers/net/wireless/realtek/rtw89/mac.c

@@ -1093,7 +1093,6 @@ static int cmac_func_en(struct rtw89_dev *rtwdev, u8 mac_idx, bool en)
 static int dmac_func_en(struct rtw89_dev *rtwdev)
 {
 	u32 val32;
-	u32 ret = 0;
 
 	val32 = (B_AX_MAC_FUNC_EN | B_AX_DMAC_FUNC_EN | B_AX_MAC_SEC_EN |
 		 B_AX_DISPATCHER_EN | B_AX_DLE_CPUIO_EN | B_AX_PKT_IN_EN |
@@ -1107,7 +1106,7 @@ static int dmac_func_en(struct rtw89_dev *rtwdev)
 		 B_AX_WD_RLS_CLK_EN);
 	rtw89_write32(rtwdev, R_AX_DMAC_CLK_EN, val32);
 
-	return ret;
+	return 0;
 }
 
 static int chip_func_en(struct rtw89_dev *rtwdev)