ieee802154: cc2520: switch from BUG_ON() to WARN_ON() on problem

The check is valid but it does not warrant to crash the kernel. A
WARN_ON() is good enough here.
Found by checkpatch.

Signed-off-by: Stefan Schmidt <[e-mail]>
Acked-by: Varka Bhadram <[e-mail]>
Signed-off-by: Stefan Schmidt <[e-mail]>

drivers/net/ieee802154/cc2520.c

···
 	}
 
 	spin_lock_irqsave(&priv->lock, flags);
-	BUG_ON(priv->is_tx);
+	WARN_ON(priv->is_tx);
 	priv->is_tx = 1;
 	spin_unlock_irqrestore(&priv->lock, flags);
 
···
 
 	dev_dbg(&priv->spi->dev, "trying to set channel\n");
 
-	BUG_ON(page != 0);
-	BUG_ON(channel < CC2520_MINCHANNEL);
-	BUG_ON(channel > CC2520_MAXCHANNEL);
+	WARN_ON(page != 0);
+	WARN_ON(channel < CC2520_MINCHANNEL);
+	WARN_ON(channel > CC2520_MAXCHANNEL);
 
 	ret = cc2520_write_register(priv, CC2520_FREQCTRL,
 				    11 + 5 * (channel - 11));