soc: qcom: glink: Fix uninitialzed return value

Initialize the return value in the glink tx scheduler
function.
CRs-Fixed: 1081425

Change-Id: I7cad7a724666f34bce73d40e4975373604fb1e87
Signed-off-by: Chris Lew <clew@codeaurora.org>
Signed-off-by: Dhoat Harpal <hdhoat@codeaurora.org>