inputs: Fix key_up/key_down mismatch
inputs: Fix key_up/key_down mismatch

When handling a KEY_UP message, the various variables were called
'key_down', and they were called 'key_up' when handling KEY_DOWN
messages. This commit makes the naming consistent.

freedesktop-unofficial-mirror/spice__spice,Fantu/spice,SPICE/spice,Fantu/spice,fgouget/spice,freedesktop-unofficial-mirror/spice__spice,freedesktop-unofficial-mirror/spice__spice,ya-mouse/spice,freedesktop-unofficial-mirror/spice__spice,Fantu/spice,fgouget/spice,fgouget/spice,SPICE/spice,ya-mouse/spice,SPICE/spice,fgouget/spice,freedesktop-unofficial-mirror/spice__spice,ya-mouse/spice,Fantu/spice