HID: intel_ish-hid: Add check for ishtp_dma_tx_map

HID: intel_ish-hid: Add check for ishtp_dma_tx_map

[ Upstream commit 5272f5495d23a2c44e96db53e23212c643c9bcad ]

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: 99cccf0d09f5 ("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>
Signed-off-by: Sasha Levin <sashal@kernel.org>