ARM: S3C24XX: Fix potential NULL pointer dereference error

chan->end is tested for being NULL. However in the event that it is NULL, the
subsequent assignment statement would lead to NULL pointer dereference.
Thus dereferencing it only when it is not NULL.
Signed-off-by: Sachin Kamat <sachin.kamat@linaro.org>
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>

arch/arm/plat-s3c24xx/dma.c

@@ -473,12 +473,13 @@ int s3c2410_dma_enqueue(enum dma_ch channel, void *id,
 		pr_debug("dma%d: %s: buffer %p queued onto non-empty channel\n",
 			 chan->number, __func__, buf);
 
-		if (chan->end == NULL)
+		if (chan->end == NULL) {
 			pr_debug("dma%d: %s: %p not empty, and chan->end==NULL?\n",
 				 chan->number, __func__, chan);
-
-		chan->end->next = buf;
-		chan->end = buf;
+		} else {
+			chan->end->next = buf;
+			chan->end = buf;
+		}
 	}
 
 	/* if necessary, update the next buffer field */