mmc: vub300: fix invalid response handling

We may get an empty response with zero length at the beginning of
the driver start and get following UBSAN error. Since there is no
content(SDRT_NONE) for the response, just return and skip the response
handling to avoid this problem.

Test pass : SDIO wifi throughput test with this patch

[  126.980684] UBSAN: array-index-out-of-bounds in drivers/mmc/host/vub300.c:1719:12
[  126.980709] index -1 is out of range for type 'u32 [4]'
[  126.980729] CPU: 4 PID: 9 Comm: kworker/u16:0 Tainted: G            E      6.3.0-rc4-mtk-local-202304272142 ljalves#1
[  126.980754] Hardware name: Intel(R) Client Systems NUC8i7BEH/NUC8BEB, BIOS BECFL357.86A.0081.2020.0504.1834 05/04/2020
[  126.980770] Workqueue: kvub300c vub300_cmndwork_thread [vub300]
[  126.980833] Call Trace:
[  126.980845]  <TASK>
[  126.980860]  dump_stack_lvl+0x48/0x70
[  126.980895]  dump_stack+0x10/0x20
[  126.980916]  ubsan_epilogue+0x9/0x40
[  126.980944]  __ubsan_handle_out_of_bounds+0x70/0x90
[  126.980979]  vub300_cmndwork_thread+0x58e7/0x5e10 [vub300]
[  126.981018]  ? _raw_spin_unlock+0x18/0x40
[  126.981042]  ? finish_task_switch+0x175/0x6f0
[  126.981070]  ? __switch_to+0x42e/0xda0
[  126.981089]  ? __switch_to_asm+0x3a/0x80
[  126.981129]  ? __pfx_vub300_cmndwork_thread+0x10/0x10 [vub300]
[  126.981174]  ? __kasan_check_read+0x11/0x20
[  126.981204]  process_one_work+0x7ee/0x13d0
[  126.981246]  worker_thread+0x53c/0x1240
[  126.981291]  kthread+0x2b8/0x370
[  126.981312]  ? __pfx_worker_thread+0x10/0x10
[  126.981336]  ? __pfx_kthread+0x10/0x10
[  126.981359]  ret_from_fork+0x29/0x50
[  126.981400]  </TASK>

Fixes: 88095e7 ("mmc: Add new VUB300 USB-to-SD/SDIO/MMC driver")
Signed-off-by: Deren Wu <deren.wu@mediatek.com>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/048cd6972c50c33c2e8f81d5228fed928519918b.1683987673.git.deren.wu@mediatek.com
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>

drivers/mmc/host/vub300.c

@@ -1713,6 +1713,9 @@ static void construct_request_response(struct vub300_mmc_host *vub300,
 	int bytes = 3 & less_cmd;
 	int words = less_cmd >> 2;
 	u8 *r = vub300->resp.response.command_response;
+
+	if (!resp_len)
+		return;
 	if (bytes == 3) {
 		cmd->resp[words] = (r[1 + (words << 2)] << 24)
 			| (r[2 + (words << 2)] << 16)