There is no /smb@4000000 node upstream any longer as it was
renamed with the 8d158e1a4091 ("dts: update to v5.7-rc1") sync.

Adjust the barebox device tree accordingly. It's likely that this
resulted in barebox v2020.06.0 state, environment and update breakage on
the vexpress boards.

Cc: Roland Hieber <rhi@pengutronix.de>
Fixes: 8d158e1a4091 ("dts: update to v5.7-rc1")
Signed-off-by: Ahmad Fatoum <a.fatoum@pengutronix.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>