Revert "firmware: stratix10-svc: release mutex sdm_lock after processing command"

This reverts commit 239adc5d.

The issue is already fixed by another SDK patch 7d97a731


("HSD #16013024105: fpga: stratix10-soc: stop kernel thread"),
Revert this one to avoid "fcs_clent -G" run failed with error:
"svc_normal_to_secure_thread: STATUS_ERROR"

Signed-off-by: Liwei Song <liwei.song@windriver.com>