msm: kgsl: Fix kgsl memory allocation and free race condition

When allocating userspace memory keep reference to memory
allocation till it is completely initialized and info is sent back
to userspace.

Bug: 32938443
Change-Id: Id72c82bf98c094ecbd4722813c732a998dcbb188
Signed-off-by: Tarun Karra <tkarra@codeaurora.org>
Signed-off-by: Sunil Khatri <sunilkh@codeaurora.org>