mfd: fix pcap adc locking

Release the lock on error.

Signed-off-by: Daniel Ribeiro <drwyrm@gmail.com>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>
diff --git a/drivers/mfd/ezx-pcap.c b/drivers/mfd/ezx-pcap.c
index 671a7ef..c1de4af 100644
--- a/drivers/mfd/ezx-pcap.c
+++ b/drivers/mfd/ezx-pcap.c
@@ -238,8 +238,10 @@
 	mutex_lock(&pcap->adc_mutex);
 	req = pcap->adc_queue[pcap->adc_head];
 
-	if (WARN(!req, KERN_WARNING "adc irq without pending request\n"))
+	if (WARN(!req, KERN_WARNING "adc irq without pending request\n")) {
+		mutex_unlock(&pcap->adc_mutex);
 		return IRQ_HANDLED;
+	}
 
 	/* read requested channels results */
 	ezx_pcap_read(pcap, PCAP_REG_ADC, &tmp);