Changed floor to ceil for system to avrcp volume

When converting to system volume, Math.floor is used, we
need to use Math.ceil to convert back so we don't loose
approximation.

Tag: #feature
Bug: 193685552
Test: atest BluetoothInstrumentationTests, manual
Change-Id: Iebae59a10d10e8f292fb7b3c873cd4f4afd395e7