[media] exynos4-is: Free FIMC-IS CPU memory only when allocated

Ensure dma_free_coherent() is not called with incorrect arguments
and only when the memory was actually allocated. This will prevent
possible crashes on error paths of the top level media device driver,
when fimc-is device gets unregistered and its driver detached.

Signed-off-by: Sylwester Nawrocki <[e-mail]>
Acked-by: Kyungmin Park <[e-mail]>
Cc: [e-mail] # for v3.15
Signed-off-by: Mauro Carvalho Chehab <[e-mail]>

drivers/media/platform/exynos4-is/fimc-is.c

···
 {
 	struct device *dev = &is->pdev->dev;
 
+	if (is->memory.vaddr == NULL)
+		return;
+
 	dma_free_coherent(dev, is->memory.size, is->memory.vaddr,
 			  is->memory.paddr);
 }