sim: riscv: Fix confusion with c.jal vs. c.addiw

There was apparently a confusion which cpu model uses
compressed JAL and which ADDIW.  Fixed that in execute_c,
case MATCH_C_JAL | MATCH_C_ADDIW.

Fixes 3224e32f ("sim: riscv: Add support for compressed integer instructions")

Approved-By: Andrew Burgess <aburgess@redhat.com>