usb: gadget: mv_u3d: replace deprecated strncpy with strscpy

usb: gadget: mv_u3d: 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.

Let's opt for the new 2-argument version of strscpy() which guarantees
NUL-termination on the destination buffer and simplifies snytax. The
NUL-padding behavior that strncpy() provides is not required as u3d->eps
is already zero-allocated:
|	u3d->eps = kzalloc(size, GFP_KERNEL);

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
Cc: linux-hardening@vger.kernel.org
Signed-off-by: Justin Stitt <justinstitt@google.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20240318-strncpy-drivers-usb-gadget-udc-mv_u3d_core-c-v1-1-64f8dcdb7c07@google.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>