qcacld-3.0: check the state before starting auto ps timer

Since sme_ps_enable_auto_ps_timer will be called in
different scenarios, and there is error level output
if trying to start it when it's already started.
To avoid the useless error log, check the state
before starting this timer.

CRs-Fixed: 2747427
Change-Id: If119da266a991b6b5990ad3077e41c2bba11a798