ath10k: avoid possible string overflow

BugLink: https://bugs.launchpad.net/bugs/1826212

commit 6707ba01 upstream.

The way that 'strncat' is used here raised a warning in gcc-8:

drivers/net/wireless/ath/ath10k/wmi.c: In function 'ath10k_wmi_tpc_stats_final_disp_tables':
drivers/net/wireless/ath/ath10k/wmi.c:4649:4: error: 'strncat' output truncated before terminating nul copying as many bytes from a string as its length [-Werror=stringop-truncation]

Effectively, this is simply a strcat() but the use of strncat() suggests
some form of overflow check. Regardless of whether this might actually
overflow, using strlcat() instead of strncat() avoids the warning and
makes the code more robust.

Fixes: bc64d052 ("ath10k: debugfs support to get final TPC stats for 10.4 variants")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>

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

@@ -4066,7 +4066,7 @@ static void ath10k_tpc_config_disp_tables(struct ath10k *ar,
 							    rate_code[i],
 							    type);
 			snprintf(buff, sizeof(buff), "%8d ", tpc[j]);
-			strncat(tpc_value, buff, strlen(buff));
+			strlcat(tpc_value, buff, sizeof(tpc_value));
 		}
 		tpc_stats->tpc_table[type].pream_idx[i] = pream_idx;
 		tpc_stats->tpc_table[type].rate_code[i] = rate_code[i];