mfd: Add export.h for EXPORT_SYMBOL/THIS_MODULE as required

These macros are in <linux/export.h> and will no longer be
implicitly everywhere anymore.  Fix it up in advance.

Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
diff --git a/drivers/mfd/asic3.c b/drivers/mfd/asic3.c
index c71ae09..7d54973 100644
--- a/drivers/mfd/asic3.c
+++ b/drivers/mfd/asic3.c
@@ -20,6 +20,7 @@
 #include <linux/delay.h>
 #include <linux/irq.h>
 #include <linux/gpio.h>
+#include <linux/export.h>
 #include <linux/io.h>
 #include <linux/slab.h>
 #include <linux/spinlock.h>