libaudiohal: Allow get/setMasterVolume invocation on IDevice

get/setMasterVolume are defined on IDevice, but DeviceHalHidl
was restricting calls to it only for IPrimaryDevice. This seems
like a bug lingering from the initial implementation of the shim.

Test: make
Change-Id: Ia028959690a5ab71aade14d12d5c12488dc83e41
1 file changed