linux-phytec-ti

drm/vmwgfx: Update comments for sou plane update function

Update comments to sync with code.

Signed-off-by: Deepak Rawat <drawat@vmware.com>
Reviewed-by: Thomas Hellstrom <thellstrom@vmware.com>
Signed-off-by: Thomas Hellstrom <thellstrom@vmware.com>