wifi: brcmfmac: work around a GCC 12 -Warray-bounds warning

GCC 12 really doesn't like partial struct allocations:

drivers/net/wireless/broadcom/brcm80211/brcmfmac/cfg80211.c:2202:32: warning: array subscript ‘struct brcmf_ext_join_params_le[0]’ is partly outside array bounds of ‘void[70]’ [-Warray-bounds]
 2202 |                 ext_join_params->scan_le.passive_time =
      |                                ^~

brcmfmac is trying to save 2 bytes at the end by either allocating
or not allocating a channel member. Let's keep @join_params_size
the "right" size but kmalloc() the full structure.
Acked-by: Kalle Valo <kvalo@kernel.org>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/wireless/broadcom/brcm80211/brcmfmac/cfg80211.c

@@ -2167,7 +2167,7 @@ brcmf_cfg80211_connect(struct wiphy *wiphy, struct net_device *ndev,
 		offsetof(struct brcmf_assoc_params_le, chanspec_list);
 	if (cfg->channel)
 		join_params_size += sizeof(u16);
-	ext_join_params = kzalloc(join_params_size, GFP_KERNEL);
+	ext_join_params = kzalloc(sizeof(*ext_join_params), GFP_KERNEL);
 	if (ext_join_params == NULL) {
 		err = -ENOMEM;
 		goto done;