openrisc: include export.h for EXPORT_SYMBOL

Use of EXPORT_SYMBOL requires inclusion of export.h

Signed-off-by: Jonas Bonn <jonas@southpole.se>
diff --git a/arch/openrisc/kernel/irq.c b/arch/openrisc/kernel/irq.c
index 59b3023..4bfead2 100644
--- a/arch/openrisc/kernel/irq.c
+++ b/arch/openrisc/kernel/irq.c
@@ -23,6 +23,7 @@
 #include <linux/irq.h>
 #include <linux/seq_file.h>
 #include <linux/kernel_stat.h>
+#include <linux/export.h>
 
 #include <linux/irqflags.h>