With the loop break like this, there are false "FFT report truncated"
messages because the iterator is not advanced as the check expects.

Instead, just return, for a single frame there is nothing left to be
done anyways.

Cc: Nick Kossifidis <mickflemm@gmail.com>
Signed-off-by: Simon Wunderlich <sw@simonwunderlich.de>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>