libertas: struct lbs_private is declared duplicately

struct lbs_private has been declared at 22nd line.
Remove the duplicate.
Signed-off-by: Wan Jiabing <wanjiabing@vivo.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20210325064154.854245-1-wanjiabing@vivo.com

drivers/net/wireless/marvell/libertas/decl.h

@@ -23,7 +23,6 @@ struct lbs_private;
 typedef void (*lbs_fw_cb)(struct lbs_private *priv, int ret,
 		const struct firmware *helper, const struct firmware *mainfw);
 
-struct lbs_private;
 struct sk_buff;
 struct net_device;
 struct cmd_ds_command;