KVM: x86: Fix wrong masking on relative jump/call

Relative jumps and calls do the masking according to the operand size, and not
according to the address size as the KVM emulator does today.

This patch fixes KVM behavior.

Cc: stable@vger.kernel.org
Signed-off-by: Nadav Amit <namit@cs.technion.ac.il>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>