RISC-V: Fix display of partial instructions

RISC-V: Fix display of partial instructions

As of commit e43d8768d909 ("RISC-V: Fix disassemble fetch fail return
value.") partial instructions are no longer displayed by objdump. While
that commit fixed the behavior of print_insn_riscv() returning the
arbitrary status value upon failure, it caused the behavior of dumping
instructions to change. Allow partial instructions to be displayed once
again and only return -1 if no part of the instruction was able to be
displayed.

Fixes: e43d8768d909 ("RISC-V: Fix disassemble fetch fail return
value.")

Signed-off-by: Charlie Jenkins <charlie@rivosinc.com>
Acked-By: Andrew Burgess <aburgess@redhat.com>