drivers/mediatek: Fix build warning

The "group" variable is set but unused, causing a -Werror build
failure with Zephyr.

Signed-off-by: Andy Ross <andyross@google.com>

Author: andyross

src/drivers/mediatek/mt8196/intc.c

@@ -52,11 +52,10 @@ void intc_init(void)
 
 void intc_irq_unmask(enum IRQn_Type irq)
 {
-	uint32_t word, group;
+	uint32_t word;
 
 	if (irq < IRQ_MAX_CHANNEL && intc_desc.irqs[irq].group < INTC_GRP_NUM) {
 		word = INTC_WORD(irq);
-		group = intc_desc.irqs[irq].group;
 		io_reg_update_bits(INTC_IRQ_EN(word), INTC_BIT(irq), INTC_BIT(irq));
 	} else {
 		tr_err(&intc_tr, "Invalid INTC interrupt %d", irq);