efi_loader: infinite recursion notifying events

UEFI SCT uses this call sequence to determine the current TPL level inside
notification functions:

    OldTpl = BS->RaiseTPL(TPL_HIGH_LEVEL);
    BS->RestoreTPL(OldTpl);

In RestoreTPL() we trigger the notification function of queued events. If
we do not mark the event as non-queued before calling the notification
function, this results in an infinite recursive call sequence.

Mark the event as non-queued before entering the notification function.

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>