[le audio] Update volume control APIs range to 0~255

Per volume control service spec, the volume range should be 0~255.

Flagged by: leaudio_broadcast_volume_control_for_connected_devices and
enable by adb command
adb shell device_config put bluetooth com.android.bluetooth.flags.leaudio_broadcast_volume_control_for_connected_devices true

Bug: 311758236
Bug: 307408418
Test: atest BluetoothVolumeControlTest
Change-Id: Ie9e753fe97274c4ed738bce0b50875cea4e773b4