HID: intel_ish-hid: Add check for ishtp_dma_tx_map

As the kcalloc may return NULL pointer,
it should be better to check the ishtp_dma_tx_map
before use in order to avoid NULL pointer dereference.

Fixes: 3703f53b ("HID: intel_ish-hid: ISH Transport layer")
Signed-off-by: Jiasheng Jiang <jiasheng@iscas.ac.cn>
Acked-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>

drivers/hid/intel-ish-hid/ishtp/dma-if.c

@@ -104,6 +104,11 @@ void *ishtp_cl_get_dma_send_buf(struct ishtp_device *dev,
 	int required_slots = (size / DMA_SLOT_SIZE)
 		+ 1 * (size % DMA_SLOT_SIZE != 0);
 
+	if (!dev->ishtp_dma_tx_map) {
+		dev_err(dev->devc, "Fail to allocate Tx map\n");
+		return NULL;
+	}
+
 	spin_lock_irqsave(&dev->ishtp_dma_tx_lock, flags);
 	for (i = 0; i <= (dev->ishtp_dma_num_slots - required_slots); i++) {
 		free = 1;
@@ -150,6 +155,11 @@ void ishtp_cl_release_dma_acked_mem(struct ishtp_device *dev,
 		return;
 	}
 
+	if (!dev->ishtp_dma_tx_map) {
+		dev_err(dev->devc, "Fail to allocate Tx map\n");
+		return;
+	}
+
 	i = (msg_addr - dev->ishtp_host_dma_tx_buf) / DMA_SLOT_SIZE;
 	spin_lock_irqsave(&dev->ishtp_dma_tx_lock, flags);
 	for (j = 0; j < acked_slots; j++) {