Only return early from data processing if it is not using data callback.

For data callback case, it is relying on the wakeup time to control the
callback is called at the right frequency to avoid xrun. In that case,
when using data callback, it should still suspend until the wakup time
even if all data has been processed.

Bug: 420739849
Test: atest AAudioTests
Test: OboeTester, test output in shared mode
Flag: EXEMPT bugfix
Change-Id: I7c3747bcb347316f403a28ee84e2f82b30494793