soc: imx: imx-scu: Getting UID from SCU should have response

The SCU firmware API for getting UID should have response,
otherwise, the message stored in function stack could be
released and then the response data received from SCU will be
stored into that released stack and cause kernel NULL pointer
dump.

Fixes: 73feb4d0 ("soc: imx-scu: Add SoC UID(unique identifier) support")
Signed-off-by: Anson Huang <Anson.Huang@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>