drm/vmwgfx: Make sure bo's are unpinned before putting them back

During cotable resize we pin the backup buffer to make sure the
trylock doesn't fail. We were never unpinning the backup buffer
resulting in every subsequent cotable resize trying to release a
pinned bo. After we copy the old backup to the new we can release
the pin.
Mob's are always pinned so we just have to make sure we unpin
them before releasing them.

Reviewed-by: Thomas Hellström (Intel) <thomas_os@shipmail.org>
Fixes: d1a73c64 ("drm/vmwgfx: Make sure we unpin no longer needed buffers")
Link: https://patchwork.freedesktop.org/patch/msgid/20210413205938.788366-1-zackr@vmware.com


Signed-off-by: Zack Rusin <zackr@vmware.com>