arm64: dts: ti: k3-am69-sk: remove assigned-clock-parents for unused VP

arm64: dts: ti: k3-am69-sk: remove assigned-clock-parents for unused VP

VP2 and VP3 are unused video ports and VP3 share the same parent
clock as VP1 causing issue with pixel clock setting for HDMI (VP1).
The current DM firmware does not support changing parent clock if it
is shared by another component. It returns 0 for the determine_rate
query before causing set_rate to set the clock at default maximum of
1.8GHz which is a lot more than the maximum frequency videoports can
support (600MHz) causing SYNC LOST issues.
So remove the parent clocks for unused VPs to avoid conflict.

Fixes: 6f8605fd7d11 ("arm64: dts: ti: k3-am69-sk: Add DP and HDMI support")
Reported-by: Nishanth Menon <nm@ti.com>
Signed-off-by: Jayesh Choudhary <j-choudhary@ti.com>
Reviewed-by: Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>
Reviewed-by: Aradhya Bhatia <a-bhatia1@ti.com>
Tested-by: Enric Balletbo i Serra <eballetbo@redhat.com>
Link: https://lore.kernel.org/r/20240201142308.4954-1-j-choudhary@ti.com
Signed-off-by: Vignesh Raghavendra <vigneshr@ti.com>