ath10k: fix backtrace on coredump

In a multiradio board with one QCA9984 and one AR9987
after enabling the crashdump with module parameter
coredump_mask=7, below backtrace is seen.

vmalloc: allocation failure: 0 bytes
 kworker/u4:0: page allocation failure: order:0, mode:0x80d2
 CPU: 0 PID: 6 Comm: kworker/u4:0 Not tainted 3.14.77 #130
 Workqueue: ath10k_wq ath10k_core_register_work [ath10k_core]
 (unwind_backtrace) from [<c021abf8>] (show_stack+0x10/0x14)
 (dump_stack+0x80/0xa0)
 (warn_alloc_failed+0xd0/0xfc)
 (__vmalloc_node_range+0x1b4/0x1d8)
 (__vmalloc_node+0x34/0x40)
 (vzalloc+0x24/0x30)
 (ath10k_coredump_register+0x6c/0x88 [ath10k_core])
 (ath10k_core_register_work+0x350/0xb34 [ath10k_core])
 (process_one_work+0x20c/0x32c)
 (worker_thread+0x228/0x360)

This is due to ath10k_hw_mem_layout is not defined for AR9987.
For coredump undefined hw ramdump_size is 0.
Check for the ramdump_size before allocation memory.

Tested on: AR9987, QCA9984
FW version: 10.4-3.9.0.2-00044
Signed-off-by: Anilkumar Kolli <akolli@codeaurora.org>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>

drivers/net/wireless/ath/ath10k/coredump.c

@@ -1229,9 +1229,11 @@ static struct ath10k_dump_file_data *ath10k_coredump_build(struct ath10k *ar)
 		dump_tlv = (struct ath10k_tlv_dump_data *)(buf + sofar);
 		dump_tlv->type = cpu_to_le32(ATH10K_FW_CRASH_DUMP_RAM_DATA);
 		dump_tlv->tlv_len = cpu_to_le32(crash_data->ramdump_buf_len);
-		memcpy(dump_tlv->tlv_data, crash_data->ramdump_buf,
-		       crash_data->ramdump_buf_len);
-		sofar += sizeof(*dump_tlv) + crash_data->ramdump_buf_len;
+		if (crash_data->ramdump_buf_len) {
+			memcpy(dump_tlv->tlv_data, crash_data->ramdump_buf,
+			       crash_data->ramdump_buf_len);
+			sofar += sizeof(*dump_tlv) + crash_data->ramdump_buf_len;
+		}
 	}
 
 	mutex_unlock(&ar->dump_mutex);
@@ -1278,6 +1280,9 @@ int ath10k_coredump_register(struct ath10k *ar)
 	if (test_bit(ATH10K_FW_CRASH_DUMP_RAM_DATA, &ath10k_coredump_mask)) {
 		crash_data->ramdump_buf_len = ath10k_coredump_get_ramdump_size(ar);
 
+		if (!crash_data->ramdump_buf_len)
+			return 0;
+
 		crash_data->ramdump_buf = vzalloc(crash_data->ramdump_buf_len);
 		if (!crash_data->ramdump_buf)
 			return -ENOMEM;