ASoC: SOF: Fix snd_sof_ipc_stream_posn()

We're passing "&posn" instead of "posn" so it ends up corrupting
memory instead of doing something useful.

Fixes: 53e0c72d

 ("ASoC: SOF: Add support for IPC IO between DSP and Host")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: Kai Vehmanen <kai.vehmanen@linux.intel.com>
Link: https://lore.kernel.org/r/20200303101858.ytehbrivocyp3cnf@kili.mountain
Signed-off-by: Mark Brown <broonie@kernel.org>