ath10k: fix the garage chars in board file name creation

The variant[] string will be valid only if the bdf_ext is set.

The string memory needs to be null-terminated to avoid the undefined garbage
appended by the subsequent board file name creation.

ath10k_pci 0000:04:00.0: failed to fetch board data for
"bus=pci,vendor=168c,device=003e,subsystem-vendor=168c,subsystem-device=3363��P�����"
from ath10k/QCA6174/hw3.0/board-2.bin

Fixes: f2593cb1 ("ath10k: Search SMBIOS for OEM board file extension")
Reported-by: Kalle Valo <kvalo@qca.qualcomm.com>
Signed-off-by: Ryan Hsu <ryanhsu@qca.qualcomm.com>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>

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

@@ -1126,7 +1126,7 @@ static int ath10k_core_create_board_name(struct ath10k *ar, char *name,
 					 size_t name_len)
 {
 	/* strlen(',variant=') + strlen(ar->id.bdf_ext) */
-	char variant[9 + ATH10K_SMBIOS_BDF_EXT_STR_LENGTH];
+	char variant[9 + ATH10K_SMBIOS_BDF_EXT_STR_LENGTH] = { 0 };
 
 	if (ar->id.bmi_ids_valid) {
 		scnprintf(name, name_len,