[webapi][XWALK-2108] update the attribute name for AudioSystemContext

- Fail Reason: the error callback is invoked.

Impacted TCs num: New 0, Update 1, Delete 0
Unit test Platform: [Tizen-IVI]
Test result summary: Pass 0, Fail 1, Blocked 0
Merge pull request #454 from JianfengXu/xujf/simd/2108

[webapi][XWALK-2108] update the attribute name for AudioSystemContext