soc: qcom: bam_dmux: exit ul_wakeup() thread in SSR case

The ul_wakeup() thread wait for ACK from modem and triggers the SSR
if the ACK is not received in time. During this wait time if modem
goes to shut down and comes up then ul_wakeup() thread cannot get the
ACK and cause the SSR again.

During the modem shutdown case exit the ul_wakeup() thread instead
of waiting for the ACK from modem.

CRs-Fixed: 1002215
Change-Id: I88440a5fb6e69ae0e058ed0b268f0d0da2591bbf
Signed-off-by: Arun Kumar Neelakantam <aneela@codeaurora.org>