msm: kgsl: Delete list entry in only one place

To prevent racing, only delete the pending message
from the list in the function that puts it in the list.
This prevents the handler from deleting it in another
thread.

CRs-Fixed: 2063062
Change-Id: Ied140ca1e76282f48c4f9b0fc7ca5f311ba6c67f
Signed-off-by: Kyle Piefer <kpiefer@codeaurora.org>