ASoC: SOF: amd: Fix NULL pointer crash in acp_sof_ipc_msg_data function

Check substream and runtime variables before assigning.

Signed-off-by: V sujith kumar Reddy <Vsujithkumar.Reddy@amd.com>
Link: https://lore.kernel.org/r/20230508070510.6100-1-Vsujithkumar.Reddy@amd.com
Signed-off-by: Mark Brown <broonie@kernel.org>