rtlwifi: rtl8192cu: trx: Demote clear abuse of kernel-doc format

Fixes the following W=1 kernel build warning(s):

 drivers/net/wireless/realtek/rtlwifi/rtl8192cu/trx.c:455: warning: Function parameter or member 'txdesc' not described in '_rtl_tx_desc_checksum'

Cc: Ping-Ke Shih <pkshih@realtek.com>
Cc: Kalle Valo <kvalo@codeaurora.org>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Jakub Kicinski <kuba@kernel.org>
Cc: Larry Finger <Larry.Finger@lwfinger.net>
Cc: linux-wireless@vger.kernel.org
Cc: netdev@vger.kernel.org
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20201102112410.1049272-6-lee.jones@linaro.org

drivers/net/wireless/realtek/rtlwifi/rtl8192cu/trx.c

@@ -448,7 +448,7 @@ static void _rtl_fill_usb_tx_desc(__le32 *txdesc)
 	set_tx_desc_first_seg(txdesc, 1);
 }
 
-/**
+/*
  *	For HW recovery information
  */
 static void _rtl_tx_desc_checksum(__le32 *txdesc)