rpmsg: Strcpy is not safe, use strscpy_pad() instead

Replace strcpy() with strscpy_pad() for copying the rpmsg
device name in rpmsg_register_device_override().

Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Saud Farooqui <farooqui_saud@hotmail.com>
Link: https://lore.kernel.org/r/PA4P189MB14210AA95DCA3715AFA7F4A68BB59@PA4P189MB1421.EURP189.PROD.OUTLOOK.COM
Signed-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>