KVM: VMX: Set msr bitmap correctly if vcpu is in guest mode

In commit 3af18d9c ("KVM: nVMX: Prepare for using hardware MSR bitmap"),
we are setting MSR_BITMAP in prepare_vmcs02 if we should use hardware. This
is not enough since the field will be modified by following vmx_set_efer.

Fix this by setting vmx_msr_bitmap_nested in vmx_set_msr_bitmap if vcpu is
in guest mode.

Signed-off-by: Wincy Van <fanwenyi0529@gmail.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>