soc: qcom: sysmon: fix mutex error in in sysmon driver

When PIL probing is deferred, data->instance_id is 0.
Hence sysmon_notifier_register exits and it unlocks the mutex
which is not locked. So lock the mutext before the first
error condition check.

Change-Id: I99b5db71de8703c95ca70141529c42fb330436e6
Signed-off-by: Se Wang (Patrick) Oh <sewango@codeaurora.org>