Staging: most: fix snprintf() is printing too much

This patch prevents snprintf from exceeding a given buffer size.

Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Christian Gromm <christian.gromm@microchip.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>