arm: mvebu: clearfog: don't override set fdtfile env

Only set the fdtfile environment variable when not already set.

Fixes: 867572f09ebe6 ("ARM: mvebu: clearfog: run-time selection of DT file")
Cc: Joel Johnson <mrjoel@lixil.net>
Reported-by: Andre Heider <a.heider@gmail.com>
Signed-off-by: Baruch Siach <baruch@tkos.co.il>
Reviewed-by: Andre Heider <a.heider@gmail.com>
1 file changed