i2c: mux: pca954x: Refactor pca954x_irq_handler()

Refactor pca954x_irq_handler() to:
  - use for_each_set_bit() macro
  - use IRQ_RETVAL() macro

Above change makes code easy to read and understand.
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Peter Rosin <peda@axentia.se>
Signed-off-by: Wolfram Sang <wsa@kernel.org>

drivers/i2c/muxes/i2c-mux-pca954x.c

@@ -327,21 +327,18 @@ static DEVICE_ATTR_RW(idle_state);
 static irqreturn_t pca954x_irq_handler(int irq, void *dev_id)
 {
 	struct pca954x *data = dev_id;
-	unsigned int child_irq;
-	int ret, i, handled = 0;
+	unsigned long pending;
+	int ret, i;
 
 	ret = i2c_smbus_read_byte(data->client);
 	if (ret < 0)
 		return IRQ_NONE;
 
-	for (i = 0; i < data->chip->nchans; i++) {
-		if (ret & BIT(PCA954X_IRQ_OFFSET + i)) {
-			child_irq = irq_linear_revmap(data->irq, i);
-			handle_nested_irq(child_irq);
-			handled++;
-		}
-	}
-	return handled ? IRQ_HANDLED : IRQ_NONE;
+	pending = (ret >> PCA954X_IRQ_OFFSET) & (BIT(data->chip->nchans) - 1);
+	for_each_set_bit(i, &pending, data->chip->nchans)
+		handle_nested_irq(irq_linear_revmap(data->irq, i));
+
+	return IRQ_RETVAL(pending);
 }
 
 static int pca954x_irq_set_type(struct irq_data *idata, unsigned int type)