spi/topcliff_pch: Fix potential NULL dereference on allocation error

In pch_spi_handle_dma, it doesn't check for NULL returns of kcalloc
so it would result in an Oops.

Fixes: c37f3c27 ("spi/topcliff_pch: DMA support")
Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Signed-off-by: Mark Brown <broonie@kernel.org>

drivers/spi/spi-topcliff-pch.c

@@ -1008,6 +1008,9 @@ static void pch_spi_handle_dma(struct pch_spi_data *data, int *bpw)
 
 	/* RX */
 	dma->sg_rx_p = kcalloc(num, sizeof(*dma->sg_rx_p), GFP_ATOMIC);
+	if (!dma->sg_rx_p)
+		return;
+
 	sg_init_table(dma->sg_rx_p, num); /* Initialize SG table */
 	/* offset, length setting */
 	sg = dma->sg_rx_p;
@@ -1068,6 +1071,9 @@ static void pch_spi_handle_dma(struct pch_spi_data *data, int *bpw)
 	}
 
 	dma->sg_tx_p = kcalloc(num, sizeof(*dma->sg_tx_p), GFP_ATOMIC);
+	if (!dma->sg_tx_p)
+		return;
+
 	sg_init_table(dma->sg_tx_p, num); /* Initialize SG table */
 	/* offset, length setting */
 	sg = dma->sg_tx_p;