drm: xlnx: zynqmp_dpsub: Clear status register ASAP

Clear status register as soon as we read it.

Addressing comments from
https://lore.kernel.org/dri-devel/beb551c7-bb7e-4cd0-b166-e9aad90c4620@ideasonboard.com/



Signed-off-by: Anatoliy Klymenko <anatoliy.klymenko@amd.com>
Reviewed-by: Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240124025402.373620-4-anatoliy.klymenko@amd.com