rockchip: rk3399: sync spl_boot_devices_tbl and boot_devices node paths

While technically not a bug, let's have some consistency in paths
returned by u-boot,spl-boot-order look-up and the one saved in
u-boot,spl-boot-device by syncing spl_boot_devices_tbl and boot_devices
node paths.

Cc: Quentin Schulz <foss+uboot@0leil.net>
Signed-off-by: Quentin Schulz <quentin.schulz@theobroma-systems.com>
Tested-by: Xavier Drudis Ferran <xdrudis@tinet.cat>
Reviewed-by: Xavier Drudis Ferran <xdrudis@tinet.cat>
Reviewed-by: Kever Yang <kever.yang@rock-chips.com>