bcm63xx_enet: replace deprecated strncpy with strscpy

bcm63xx_enet: 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.

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

bcm_enet_get_drvinfo() already uses strscpy(), let's match it's
implementation:
|       static void bcm_enet_get_drvinfo(struct net_device *netdev,
|       				 struct ethtool_drvinfo *drvinfo)
|       {
|       	strscpy(drvinfo->driver, bcm_enet_driver_name, sizeof(drvinfo->driver));
|       	strscpy(drvinfo->bus_info, "bcm63xx", sizeof(drvinfo->bus_info));
|       }

Note that now bcm_enet_get_drvinfo() and bcm_enetsw_get_drvinfo() do the
exact same thing.

Link: https://www.kernel.org/doc/html/latest/process/deprecated.html#strncpy-on-nul-terminated-strings
Link: https://manpages.debian.org/testing/linux-manual-4.8/strscpy.9.en.html
Link: https://github.com/KSPP/linux/issues/90
Signed-off-by: Justin Stitt <justinstitt@google.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20231005-strncpy-drivers-net-ethernet-broadcom-bcm63xx_enet-c-v1-1-6823b3c3c443@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>