extcon: rt8973a: fix handling regmap_irq_get_virq result

The function can return negative value.

The problem has been detected using proposed semantic patch
scripts/coccinelle/tests/assign_signed_to_unsigned.cocci [1].

[1]: http://permalink.gmane.org/gmane.linux.kernel/2046107Signed-off-by: Andrzej Hajda <a.hajda@samsung.com>
Signed-off-by: Chanwoo Choi <cw00.choi@samsung.com>

drivers/extcon/extcon-rt8973a.c

@@ -594,7 +594,7 @@ static int rt8973a_muic_i2c_probe(struct i2c_client *i2c,
 
 	for (i = 0; i < info->num_muic_irqs; i++) {
 		struct muic_irq *muic_irq = &info->muic_irqs[i];
-		unsigned int virq = 0;
+		int virq = 0;
 
 		virq = regmap_irq_get_virq(info->irq_data, muic_irq->irq);
 		if (virq <= 0)