udmabuf: actually unmap the scatterlist

unmap_udmabuf fails to actually unmap the scatterlist, leaving dangling
mappings around.

Fixes: fbb0de795078 ("Add udmabuf misc device")
Signed-off-by: Lucas Stach <[e-mail]>
Link: http://patchwork.freedesktop.org/patch/msgid/[e-mail]
Signed-off-by: Gerd Hoffmann <[e-mail]>

drivers/dma-buf/udmabuf.c

···
 			  struct sg_table *sg,
 			  enum dma_data_direction direction)
 {
+	dma_unmap_sg(at->dev, sg->sgl, sg->nents, direction);
 	sg_free_table(sg);
 	kfree(sg);
 }