irqdomain: export irq_domain_add_simple

All other irq_domain_add_* functions are exported already, and apparently
this one got left out by mistake, which causes build errors for ARM
allmodconfig kernels:

ERROR: "irq_domain_add_simple" [drivers/gpio/gpio-rcar.ko] undefined!
ERROR: "irq_domain_add_simple" [drivers/gpio/gpio-em.ko] undefined!

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Simon Horman <horms+renesas@verge.net.au>
Signed-off-by: Grant Likely <grant.likely@linaro.org>
diff --git a/kernel/irq/irqdomain.c b/kernel/irq/irqdomain.c
index 5a83dde..d1adaed 100644
--- a/kernel/irq/irqdomain.c
+++ b/kernel/irq/irqdomain.c
@@ -191,6 +191,7 @@
 	/* A linear domain is the default */
 	return irq_domain_add_linear(of_node, size, ops, host_data);
 }
+EXPORT_SYMBOL_GPL(irq_domain_add_simple);
 
 /**
  * irq_domain_add_legacy() - Allocate and register a legacy revmap irq_domain.