drivers/dma: Add export.h to ste_dma40.c

Signed-off-by: Paul Gortmaker <[e-mail]>

drivers/dma/ste_dma40.c

···
 #include <linux/dma-mapping.h>
 #include <linux/kernel.h>
 #include <linux/slab.h>
+#include <linux/export.h>
 #include <linux/dmaengine.h>
 #include <linux/platform_device.h>
 #include <linux/clk.h>