GenericSource: restore mLock state in error cases

initFromDataSource and onPrepareAsync are called with mLock acquired.
When initFromDataSource returns with error, notifyPreparedAndCleanup
will be called and it requires mLock acquired.

Test: cts
Bug: 122564587
Change-Id: I430dbc5f1f30c06223ea22438282bd388174f7df
1 file changed