ath9k: Fix NULL pointer dereference on early irq

The ah struct might not have been initialized when
interrupt comes so check for it.

Signed-off-by: Wojciech Dubowik <[email protected]>
Signed-off-by: John W. Linville <[email protected]>

Author: Wojciech Dubowik

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

@@ -513,7 +513,7 @@ irqreturn_t ath_isr(int irq, void *dev)
 	 * touch anything. Note this can happen early
 	 * on if the IRQ is shared.
 	 */
-	if (test_bit(ATH_OP_INVALID, &common->op_flags))
+	if (!ah || test_bit(ATH_OP_INVALID, &common->op_flags))
 		return IRQ_NONE;
 
 	/* shared irq, not for us */