soc: qcom: smp2p_sleepstate: Unregister pm_notifer in error path

Unregister pm_notifer to avoid looping in register callback in the
second trial. Also change prints to use dev_* variants.

Change-Id: I017beffbd149f3182be605d90c077c1742c6b440
Signed-off-by: Arun KS <arunks@codeaurora.org>