rockchip: doc: Fix U-Boot proper location for falcon

This patch fixed U-Boot proper location has been
missed to update in bewlo commit
"rockchip: doc: update U-Boot location info"
(sha1: 73e6dbe8)

Signed-off-by: Jagan Teki <jagan@amarulasolutions.com>
Acked-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>
Reviewed-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>