regalloc/debug: fix buggy print_hard_reg_set

regalloc/debug: fix buggy print_hard_reg_set

* ira-conflicts.c (print_hard_reg_set): Correct output for sets
including FIRST_PSEUDO_REGISTER - 1.
* ira-color.c (print_hard_reg_set): Ditto.

Before, for a target with FIRST_PSEUDO_REGISTER 20, you'd get "19-18"
for (1<<19).  For (1<<18)|(1<<19), you'd get "18".

I was using ira-conflicts.c:print_hard_reg_set with a local
patch to gdbinit.in in a debug-session, and noticed the
erroneous output.  I see there's an almost identical function in
ira-color.c and on top of that, there's another function by the
same name and with similar semantics in sel-sched-dump.c, but
the last one doesn't try to print ranges.