[BBQ] Only wait when acquiring a buffer if in a sync.

There's no need to do the explicit maxBuffersAcquired check since the
acquireBuffer call will return a status of NO_BUFFER_AVAILABLE if it
can't acquire any more buffers. Therefore, the code can be simplified so
it will return early in most cases if NO_BUFFER_AVAILABLE is returned.
If there was a request to sync the buffer, then we need to wait on a
free buffer and not return early.

Test: BBQ syncs
Bug: 263340543
Bug: 263570429
Change-Id: I11a81a440bc0d22ba85bcf4d4a068b853ca5cf9c
Merged-In: I11a81a440bc0d22ba85bcf4d4a068b853ca5cf9c