KVM: x86 emulator: fix byte-sized MOVZX/MOVSX

KVM: x86 emulator: fix byte-sized MOVZX/MOVSX

(cherry picked from commit 361cad2b50a2c92b91b6f568db860fabad3bf149)

Commit 2adb5ad9fe1 removed ByteOp from MOVZX/MOVSX, replacing them by
SrcMem8, but neglected to fix the dependency in the emulation code
on ByteOp.  This caused the instruction not to have any effect in
some circumstances.

Fix by replacing the check for ByteOp with the equivalent src.op_bytes == 1.

Signed-off-by: Avi Kivity <avi@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>