update_zone: check power of zone being updated for multi-channel audio channel level update

[crowbarz]

See comment in #39 on aiopioneer/pioneer_avr.py line 1209

[crowbarz]

I'm not sure there are too many folks using AVRs that support multi-channel audio on more than one zone.

[pantherale0]

@crowbarz I remember this piece of code, from the spec sheets I was working with at the time, the command only worked on zone 1 as other zones did not have multichannel audio support.

In fact, I'm not sure I remember seeing any reference to other zones supporting more than 2 channels. Z2/Z3 for me are 2 channel only (via RCA or speaker outputs) and HDZ is entirely different anyway with no dedicated outputs apart from the hdmi port.