Input: do not pass injected events back to the originating handler

Sometimes input handlers (as opposed to input devices) have a need to
inject (or re-inject) events back into input core. For example sysrq
filter may want to inject previously suppressed Alt-SysRq so that user
can take a screen print. In this case we do not want to pass such events
back to the same same handler that injected them to avoid loops.

Signed-off-by: Dmitry Torokhov <dtor@mail.ru>