irqchip/loongson-pch-ms: Use bitmap_free() to free bitmap

kfree() and bitmap_free() are the same. But using the latter is more
consistent when freeing memory allocated with bitmap_zalloc().

Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/0b982ab54844803049c217b2899baa59602faacd.1640529916.git.christophe.jaillet@wanadoo.fr

drivers/irqchip/irq-loongson-pch-msi.c

@@ -241,7 +241,7 @@ static int pch_msi_init(struct device_node *node,
 	return 0;
 
 err_map:
-	kfree(priv->msi_map);
+	bitmap_free(priv->msi_map);
 err_priv:
 	kfree(priv);
 	return ret;