KVM: x86 emulator: Fix x86_emulate_insn() not to use the variable rc for non-X86EMUL values

This patch makes non-X86EMUL_* family functions not to use
the variable rc.

Be sure that this changes nothing but makes the purpose of
the variable rc clearer.

Signed-off-by: Takuya Yoshikawa <yoshikawa.takuya@oss.ntt.co.jp>
Signed-off-by: Avi Kivity <avi@redhat.com>