KVM: x86 emulator: do not adjust the address for immediate source

adjust the dst address for a register source but not adjust the
address for an immediate source.

Signed-off-by: Wei Yongjun <yjwei@cn.fujitsu.com>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Avi Kivity <avi@redhat.com>