bes2600: replace a set of atomic_add()

Backport of cw1200 mainline commit 07f995ca1951 ("cw1200: replace a set
of atomic_add()", 2020-11-10).  atomic_inc() reads more naturally than
atomic_add(1, &x).  Mechanical change, no functional impact.

7 sites: 6 in bh.c (bh_term, bh_rx x2, bh_tx x3) and 1 in itp.c
(awaiting_confirm).  Two of the bh_rx and three of the bh_tx sites are
inside the cw1200-ancestor #if 0 block; replaced anyway to keep the
file consistent with cw1200 mainline source style.

Cherry-picked from upstream Linux:
  07f995ca1951 cw1200: replace a set of atomic_add()
  Author: Yejune Deng <yejune.deng@gmail.com>
  Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
  Link: https://lore.kernel.org/r/1604991491-27908-1-git-send-email-yejune.deng@gmail.com

bes2600/itp.c

@@ -570,7 +570,7 @@ int bes2600_itp_get_tx(struct bes2600_common *priv, u8 **data,
 	*burst = 2;
 	atomic_set(&priv->bh_tx, 1);
 	ktime_get_ts(&itp->last_sent);
-	atomic_add(1, &itp->awaiting_confirm);
+	atomic_inc(&itp->awaiting_confirm);
 	spin_unlock_bh(&itp->tx_lock);
 	return 1;