dma: ste_dma40: Fix potential null pointer dereference

kcalloc can return NULL. Check the pointer before dereferencing.
Signed-off-by: Sachin Kamat <sachin.kamat@linaro.org>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>

drivers/dma/ste_dma40.c

@@ -2591,6 +2591,9 @@ dma40_prep_dma_cyclic(struct dma_chan *chan, dma_addr_t dma_addr,
 	int i;
 
 	sg = kcalloc(periods + 1, sizeof(struct scatterlist), GFP_NOWAIT);
+	if (!sg)
+		return NULL;
+
 	for (i = 0; i < periods; i++) {
 		sg_dma_address(&sg[i]) = dma_addr;
 		sg_dma_len(&sg[i]) = period_len;