evdev: fix uninitialised pointer value
evdev: fix uninitialised pointer value

==30224== Conditional jump or move depends on uninitialised value(s)
==30224==    at 0x40EE3A0: evdev_flush_motion (evdev.c:284)
==30224==    by 0x40EE6DC: evdev_input_device_data (evdev.c:352)
==30224==    by 0x4034710: wl_event_source_fd_dispatch (event-loop.c:76)
==30224==    by 0x4035171: wl_event_loop_dispatch (event-loop.c:462)
==30224==    by 0x4032F76: wl_display_run (wayland-server.c:785)
==30224==    by 0x8050972: main (compositor.c:2183)

Signed-off-by: Tiago Vignatti <f080760b2054d506aacc8dee97f8804c19fbc3aa@intel.com>

krezovic/weston,Tarnyko/weston-xdg_surface_present,Fantu/compositor-spice,Tarnyko/weston-xdg_surface_present,krezovic/weston,Fantu/compositor-spice,Gnurou/weston,mchalupa/weston,xorgy/weston,udoprog/weston,eyolfson/weston,giucam/weston,Gnurou/weston,giucam/weston,mchalupa/weston,eyolfson/weston,Fantu/compositor-spice,sir-murray/weston,udoprog/weston,jonnylamb/weston,jonnylamb/weston,kwm81/weston,sir-murray/weston,kwm81/weston,xorgy/weston