soc: qcom: glink: Validate ctx before using

Glink does not validate the received handle from client apis.
This leads to possibility of illegal memeory access.

Magic number is added along with rcu lock to validate handle
received from client.

CRs-Fixed: 1047743
Change-Id: I08c854d5885672cbe5410efe0736640b55de8bbb
Signed-off-by: Dhoat Harpal <hdhoat@codeaurora.org>