Input: MT - make slot assignment work for overcovered solutions

The recent inclusion of a deassignment cost in the slot assignment
algorithm did not properly account for the corner cases where the
solutions are overcovered. This change makes sure the resulting
assignment is unique, allocating new slots when necessary.

Signed-off-by: Henrik Rydberg <rydberg@bitmath.org>
Signed-off-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
Acked-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>