net: wwan: replace deprecated strncpy with strscpy

net: wwan: 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 chinfo.name to be NUL-terminated based on its use with format
strings and sprintf:
rpmsg/rpmsg_char.c
165:            dev_err(dev, "failed to open %s\n", eptdev->chinfo.name);
368:    return sprintf(buf, "%s\n", eptdev->chinfo.name);

... and with strcmp():
|  static struct rpmsg_endpoint *qcom_glink_create_ept(struct rpmsg_device *rpdev,
|  						    rpmsg_rx_cb_t cb,
|  						    void *priv,
|  						    struct rpmsg_channel_info
|  									chinfo)
|  ...
|  const char *name = chinfo.name;
|  ...
|  		if (!strcmp(channel->name, name))

Since chinfo is initialized as such (just above the strscpy()):

|       struct rpmsg_channel_info chinfo = {
|               .src = rpwwan->rpdev->src,
|               .dst = RPMSG_ADDR_ANY,
|       };

... we know other members are zero-initialized. This means no
NUL-padding is required (as any NUL-byte assignments are redundant).

Considering the above, a suitable replacement is `strscpy` 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
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/20231019-strncpy-drivers-net-wwan-rpmsg_wwan_ctrl-c-v2-1-ecf9b5a39430@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>