drm: Put damage blob when destroy plane state

Somehow the code to put the damage blob on destroy plane state and set
the blob to NULL when duplicate plane state was not merged. May be
because the files are refactored since the patch was written. With this
fix add those.

Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Deepak Rawat <drawat@vmware.com>
Reviewed-by: Thomas Hellstrom <thellstrom@vmware.com>
Fixes: d3b21767 ("drm: Add a new plane property to send damage during plane update")
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20181221193559.4346-1-drawat@vmware.com