qcom: ssr: Abort SSR when called on an offline subsystem

Currently, if SSR is triggered on a subsystem that is offline,
a kernel panic is triggered. Instead of restarting the whole
device, print a warning and abort the SSR process.

Change-Id: Ib0e03a0527002fbaa847ada491b5d43c9b0c4ff8
Signed-off-by: Deepak Katragadda <dkatraga@codeaurora.org>