[astro][buttons] Mute button is not inverted

Remove the inverted flag from the Mute button
so the button is 1 when the mic is muted
and 0 when the mic is not muted.

TEST: Manually tested that the mute button
      value corresponded to the mute
      button state.

ZX-3996 #done

Change-Id: Ia312c98987145099d8f26030502476b2cc8b0451