dt-bindings: net: sparx5: correct LAN969x register space windows

dt-bindings: net: sparx5: correct LAN969x register space windows

LAN969x needs only 2 register space windows as GCB is already covered by
the "devices" register space window, so expect only 2 "reg" and "reg-names"
properties.

Fixes: 41c6439fdc2b ("dt-bindings: net: add compatible strings for lan969x targets")
Signed-off-by: Robert Marko <robert.marko@sartura.hr>
Acked-by: Conor Dooley <conor.dooley@microchip.com>
Link: https://patch.msgid.link/20250925132109.583984-1-robert.marko@sartura.hr
Signed-off-by: Jakub Kicinski <kuba@kernel.org>