wifi: ath10k: replace deprecated strncpy with memcpy

strncpy() is deprecated [1] and we should prefer less ambiguous
interfaces.

In this case, arvif->u.ap.ssid has its length maintained by
arvif->u.ap.ssid_len which indicates it may not need to be
NUL-terminated. Make this explicit with __nonstring and use a plain old
memcpy.

This is also consistent with future copies into arvif->u.ap.ssid:

	if (changed & BSS_CHANGED_SSID &&
	    vif->type == NL80211_IFTYPE_AP) {
		arvif->u.ap.ssid_len = vif->cfg.ssid_len;
		if (vif->cfg.ssid_len)
			memcpy(arvif->u.ap.ssid, vif->cfg.ssid,
			       vif->cfg.ssid_len);
		arvif->u.ap.hidden_ssid = info->hidden_ssid;
	}

Link: https://www.kernel.org/doc/html/latest/process/deprecated.html#strncpy-on-nul-terminated-strings [1]
Link: https://github.com/KSPP/linux/issues/90


Cc: linux-hardening@vger.kernel.org
Signed-off-by: Justin Stitt <justinstitt@google.com>
Acked-by: Jeff Johnson <quic_jjohnson@quicinc.com>
Signed-off-by: Kalle Valo <quic_kvalo@quicinc.com>
Link: https://lore.kernel.org/r/20231024-strncpy-drivers-net-wireless-ath-ath10k-mac-c-v2-1-4c1f4cd4b4df@google.com