arm/imx/gpio: remove a BUG_ON in hot path

Now if the problem occurs that triggered the BUG_ON before, the machine
runs in a NULL pointer dereference.  So it wouldn't be much harder now
to debug the situation if it occured.
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>

arch/arm/plat-mxc/gpio.c

@@ -162,8 +162,6 @@ static void mxc_gpio_irq_handler(struct mxc_gpio_port *port, u32 irq_stat)
 	while (irq_stat != 0) {
 		int irqoffset = fls(irq_stat) - 1;
 
-		BUG_ON(!(irq_desc[gpio_irq_no_base + irqoffset].handle_irq));
-
 		if (port->both_edges & (1 << irqoffset))
 			mxc_flip_edge(port, irqoffset);