staging: most: sound: replace snprintf with strscpy

Using snprintf without a format specifier is potentially risky if
the string device_name contains format specifiers. Replace this with
the safer and more efficient strscpy.

Cleans up clang warning:
drivers/staging/most/sound/sound.c:673:41: warning: format string is not
a string literal (potentially insecure) [-Wformat-security]

Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>