KVM: X86 emulator: fix source operand decoding for 8bit mov[zs]x instructions

commit 660696d1 upstream.

Source operand for one byte mov[zs]x is decoded incorrectly if it is in
high byte register. Fix that.

Signed-off-by: Gleb Natapov <gleb@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>