rockchip: rk3399: boot_devices: fix eMMC node name

rockchip: rk3399: boot_devices: fix eMMC node name

When idbloader.img is flashed on the eMMC, the SPL still tries to load
from SPI-NOR first.

This is due to an incorrect look-up in the Device Tree. Since commit
822556a93459 ("arm: dts: sync the Rockhip 3399 SoCs from Linux"), the
node name (but not label) changed from sdhci@fe330000 to mmc@fe330000
meaning U-Boot SPL is not looking for the correct node name anymore and
fails to find the "same-as-spl" node when eMMC is the medium from which
the SPL booted.

Fixes: 822556a93459 ("arm: dts: sync the Rockhip 3399 SoCs from Linux")
Cc: Quentin Schulz <foss+uboot@0leil.net>
Signed-off-by: Quentin Schulz <quentin.schulz@theobroma-systems.com>
Reviewed-by: Xavier Drudis Ferran <xdrudis@tinet.cat>
Reviewed-by: Artem Lapkin  <email2tema@gmail.com>
Tested-by: Artem Lapkin  <email2tema@gmail.com>
Tested-by: Lapkin Artem <email2tema@gmail.com>
Tested-by: Lapkin Artem <email2tema@gmail.com>
Reviewed-by: Kever Yang <kever.yang@rock-chips.com>