ARM: renesas: Align env eMMC device number with Linux 6.5.3 DT changes on R-Car Gen3 Salvator-X

Set U-Boot environment storage eMMC device number to 0, to match
the new additions to DT /aliases node pulled in alongside Linux
6.5.3 DT synchronization.

Signed-off-by: Marek Vasut <marek.vasut+renesas@mailbox.org>