irqchip/gic-v3-its: Remove the redundant set_bit for lpi_map

We try to find a free LPI region in device's lpi_map and allocate them
(set them to 1) when we want to allocate LPIs for this device. This is
what bitmap_find_free_region() has done for us. The following set_bit
is redundant and a bit confusing (since we only set_bit against the first
allocated LPI idx). Remove it, and make the set_bit explicit by comment.
Signed-off-by: Zenghui Yu <yuzenghui@huawei.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>

drivers/irqchip/irq-gic-v3-its.c

@@ -2464,6 +2464,7 @@ static int its_alloc_device_irq(struct its_device *dev, int nvecs, irq_hw_number
 {
 	int idx;
 
+	/* Find a free LPI region in lpi_map and allocate them. */
 	idx = bitmap_find_free_region(dev->event_map.lpi_map,
 				      dev->event_map.nr_lpis,
 				      get_count_order(nvecs));
@@ -2471,7 +2472,6 @@ static int its_alloc_device_irq(struct its_device *dev, int nvecs, irq_hw_number
 		return -ENOSPC;
 
 	*hwirq = dev->event_map.lpi_base + idx;
-	set_bit(idx, dev->event_map.lpi_map);
 
 	return 0;
 }