The condition & swap code decoder only checks known bits and sets
based on that. If the variable is out of range, it ends up returning
uninitialized data. Turn that case into a hard error.
This fixes build warnings like:
sim/cris/semcrisv10f-switch.c:13115:11: error:
variable 'tmp_condres' is used uninitialized whenever 'if' condition is false [-Werror,-Wsometimes-uninitialized]