imx-drm: ipuv3-plane: fix plane updates for active planes

While the DMA channel is running, it is not allowed to change anything
but the inactive (double) buffer base address, so resizing a plane or
changing to a frame buffer with different pixel format is not possible.

Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>