uinput: change strcpy/strcat usage for snprintf

uinput: change strcpy/strcat usage for snprintf

Better protection against buffer overflow, though by the time someone
is manipulating your sysfs, libevdev is unlikely to be the biggest worry.

Slight change in functionality: before we checked the timestamp of
/sys/devices/virtual/input/inputXYZ before looking at /inputXYZ/name, now we
just check the name file for the timestamp.

Change-Id: I71c9240e254b534ac0aed62bc51871a18c3a0666
Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>
Reviewed-by: Benjamin Tissoires <benjamin.tissoires@gmail.com>