drm/msm/adreno: Name the shadow buffer

This was the one GPU related kernel buffer which was not given a debug
name.  Let's fix that.

Signed-off-by: Rob Clark <robdclark@chromium.org>
Link: https://lore.kernel.org/r/20211115191514.310472-1-robdclark@gmail.com


Signed-off-by: Rob Clark <robdclark@chromium.org>