ASoC: qcom: qdsp6: Reject pointer operations on unconfigured streams

The QDSP6 driver reports the current byte offset by dividing the current
copied data total by pcm_size, but pcm_size is only configured as part of
set_params() so if we manage to do a pointer operation before that happens
we will divide by 0. There is no sensible reason to do so, add an error
check for robustness.

Reported-by: Péter Ujfalusi <peter.ujfalusi@linux.intel.com>
Signed-off-by: Mark Brown <broonie@kernel.org>