KVM: riscv: selftests: Fix get-reg-list print_reg defaults

print_reg() will print everything it knows when it encounters
a register ID it's unfamiliar with in the default cases of its
decoding switches. Fix several issues with these (until now,
never tested) paths; missing newlines in printfs, missing
complement operator in mask, and missing return in order to
avoid continuing to decode.

Fixes: 62d0c458 ("KVM: riscv: selftests: get-reg-list print_reg should never fail")
Signed-off-by: Andrew Jones <ajones@ventanamicro.com>
Reviewed-by: Haibo Xu <haibo1.xu@intel.com>
Signed-off-by: Anup Patel <anup@brainfault.org>