ath9k: work around false-positive gcc warning

gcc-10 shows a false-positive warning with CONFIG_KASAN:

drivers/net/wireless/ath/ath9k/dynack.c: In function 'ath_dynack_sample_tx_ts':
include/linux/etherdevice.h:290:14: warning: writing 4 bytes into a region of size 0 [-Wstringop-overflow=]
  290 |  *(u32 *)dst = *(const u32 *)src;
      |  ~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~

Until gcc is fixed, work around this by using memcpy() in place
of ether_addr_copy(). Hopefully gcc-11 will not have this problem.

Link: https://godbolt.org/z/sab1MK
Link: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97490
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
[kvalo@codeaurora.org: remove ifdef and add a comment]
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20201026213040.3889546-8-arnd@kernel.org

drivers/net/wireless/ath/ath9k/dynack.c

@@ -246,8 +246,12 @@ void ath_dynack_sample_tx_ts(struct ath_hw *ah, struct sk_buff *skb,
 	ridx = ts->ts_rateindex;
 
 	da->st_rbf.ts[da->st_rbf.t_rb].tstamp = ts->ts_tstamp;
-	ether_addr_copy(da->st_rbf.addr[da->st_rbf.t_rb].h_dest, hdr->addr1);
-	ether_addr_copy(da->st_rbf.addr[da->st_rbf.t_rb].h_src, hdr->addr2);
+
+	/* ether_addr_copy() gives a false warning on gcc-10 so use memcpy()
+	 * https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97490
+	 */
+	memcpy(da->st_rbf.addr[da->st_rbf.t_rb].h_dest, hdr->addr1, ETH_ALEN);
+	memcpy(da->st_rbf.addr[da->st_rbf.t_rb].h_src, hdr->addr2, ETH_ALEN);
 
 	if (!(info->status.rates[ridx].flags & IEEE80211_TX_RC_MCS)) {
 		const struct ieee80211_rate *rate;