soc: qcom: Acquire mutex before checking for service

Acquire lock before you check if the service exist. This leads to
race condition where you end up adding same service multiple times
in service_list and make multiple registration request to servreg.

CRs-Fixed: 1078753
Change-Id: I8ae92ee1d26bd6687b6b2b4cbed1032485d7450e
Signed-off-by: Puja Gupta <pujag@codeaurora.org>