The accel/ code only accesses the MachineState::accel field.
As we simply want to access the accelerator, not the machine,
add a current_accel() wrapper.

Suggested-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: Cornelia Huck <cohuck@redhat.com>
Message-Id: <20200121110349.25842-9-philmd@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>