msm: kgsl: Use the correct pointer for preemption records

When we moved to the dynamic model for global buffers in
commit 2f23b00d ("msm: kgsl: Move globals to the KGSL device handle")
we missed two references to the memdescs in the snapshot code and were
accidentally passing a pointer to a pointer and copying the wrong memory.

Change-Id: Ic0dedbadc390661ecc02980990ec9ab6df731c56
Signed-off-by: Jordan Crouse <jcrouse@codeaurora.org>