soc: qcom: wda: Fix invalid memory access

Flush powersave workqueue when 5G QMI DFC service is down to
avoid a race condition that powersave work still access the QMI
handle that is being freed.

CRs-fixed: 2387468
Change-Id: I18294939fc629b9cf902e346356d071603080a18
Acked-by: Weiyi Chen <weiyic@qti.qualcomm.com>
Signed-off-by: Subash Abhinov Kasiviswanathan <subashab@codeaurora.org>