wifi: wlcore: main: replace deprecated strncpy with strscpy

strncpy() is deprecated for use on NUL-terminated destination strings
[1] and as such we should prefer more robust and less ambiguous string
interfaces.

We expect fw_version strings to be NUL-terminated based on other similar
assignments:

wireless/broadcom/brcm80211/brcmsmac/main.c
7867:           snprintf(wlc->wiphy->fw_version,
7868:                    sizeof(wlc->wiphy->fw_version), "%u.%u", rev, patch);

wireless/broadcom/b43legacy/main.c
1765:   snprintf(wiphy->fw_version, sizeof(wiphy->fw_version), "%u.%u",

wireless/broadcom/b43/main.c
2730:   snprintf(wiphy->fw_version, sizeof(wiphy->fw_version), "%u.%u",

wireless/intel/iwlwifi/dvm/main.c
1465:   snprintf(priv->hw->wiphy->fw_version,
1466:            sizeof(priv->hw->wiphy->fw_version),

wireless/intel/ipw2x00/ipw2100.c
5905:   snprintf(info->fw_version, sizeof(info->fw_version), "%s:%d:%s",

Based on this, NUL-padding is not required.

A suitable replacement is `strscpy` [2] due to the fact that it
guarantees NUL-termination on the destination buffer without
unnecessarily NUL-padding.

Link: https://www.kernel.org/doc/html/latest/process/deprecated.html#strncpy-on-nul-terminated-strings [1]
Link: https://manpages.debian.org/testing/linux-manual-4.8/strscpy.9.en.html [2]
Link: https://github.com/KSPP/linux/issues/90
Cc: linux-hardening@vger.kernel.org
Signed-off-by: Justin Stitt <justinstitt@google.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/20231018-strncpy-drivers-net-wireless-ti-wlcore-main-c-v1-1-1b1055f482a1@google.com