efi_loader: incorrect return value form DisconnectController

DisconnectController() should never return EFI_NOT_FOUND.
If EFI_DRIVER_BINDING_PROTOCOL.Stop() fails, return EFI_DEVICE_ERROR.

If the driver handle does not expose the EFI_DRIVER_BINDING_PROTOCOL
return EFI_INVALID_PARAMETER.

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>