gpio: fix pca953x set_type 'scheduling while atomic' bug

Bill Gatliff reported the following bug when using the irq_chip facility
of the pca953x driver on a PPC platform:

BUG: scheduling while atomic: insmod/1530/0x00000002

He traced it back to an i2c transaction in pca953x_irq_set_type(), which
can be called with interrupt disabled (from __setup_irq()). As the i2c
controller can sleep while sending a message, this qualifies as a bad
idea.

This patch moves the i2c transaction to pca953x_irq_bus_sync_unlock(),
where it is actually safe to send an i2c message.

[[e-mail]: coding-style fixes]
Signed-off-by: Marc Zyngier <[e-mail]>
Reported-by: Bill Gatliff <[e-mail]>
Cc: Eric Miao <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

drivers/gpio/pca953x.c

···
 static void pca953x_irq_bus_sync_unlock(unsigned int irq)
 {
 	struct pca953x_chip *chip = get_irq_chip_data(irq);
+	uint16_t new_irqs;
+	uint16_t level;
+
+	/* Look for any newly setup interrupt */
+	new_irqs = chip->irq_trig_fall | chip->irq_trig_raise;
+	new_irqs &= ~chip->reg_direction;
+
+	while (new_irqs) {
+		level = __ffs(new_irqs);
+		pca953x_gpio_direction_input(&chip->gpio_chip, level);
+		new_irqs &= ~(1 << level);
+	}
 
 	mutex_unlock(&chip->irq_lock);
 }
···
 	else
 		chip->irq_trig_raise &= ~mask;
 
-	return pca953x_gpio_direction_input(&chip->gpio_chip, level);
+	return 0;
 }
 
 static struct irq_chip pca953x_irq_chip = {