staging: wfx: simplify API coherency check

The 'channel' argument of hif_join() should never be NULL. hif_join()
does not have the responsibility to recover bug of caller.

In current code, if the argument channel is NULL, memory leaks. The new
code just emit a warning and does not give the illusion that it is
supported (and indeed a Oops will probably raise a few lines below).
Signed-off-by: Jérôme Pouiller <jerome.pouiller@silabs.com>
Link: https://lore.kernel.org/r/20210913130203.1903622-13-Jerome.Pouiller@silabs.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/wfx/hif_tx.c

@@ -301,8 +301,6 @@ int hif_join(struct wfx_vif *wvif, const struct ieee80211_bss_conf *conf,
 	WARN_ON(!conf->basic_rates);
 	WARN_ON(sizeof(body->ssid) < ssidlen);
 	WARN(!conf->ibss_joined && !ssidlen, "joining an unknown BSS");
-	if (WARN_ON(!channel))
-		return -EINVAL;
 	if (!hif)
 		return -ENOMEM;
 	body->infrastructure_bss_mode = !conf->ibss_joined;