Input: uinput - fix crash when mixing old and new init style

If user tries to initialize uinput device mixing old and new style
initialization (i.e. using old UI_SET_ABSBIT instead of UI_ABS_SETUP,
we forget to allocate input->absinfo and will crash when trying to send
absolute events:

        ioctl(ui, UI_DEV_SETUP, &us);
        ioctl(ui, UI_SET_PHYS, "Test");

        ioctl(ui, UI_SET_EVBIT, EV_ABS);
        ioctl(ui, UI_SET_ABSBIT, ABS_X);
        ioctl(ui, UI_SET_ABSBIT, ABS_Y);
        ioctl(ui, UI_DEV_CREATE, 0);

Reported-by: Rodrigo Rivas Costa <rodrigorivascosta@gmail.com>
Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=191811
Fixes: fbae10db

 ("Input: uinput - rework ABS validation")
Reviewed-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
Cc: stable@vger.kernel.org
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>