env: Don't show "Failed" error message
"Failed" error message from env_load() only clutters the log with
unnecessary details, as we already have all needed warnings by that
time. Example:
Loading Environment from FAT... MMC: no card present
** Bad device mmc 0 **
Failed (-5)
Let's only print it in case when DEBUG is defined to keep log clear.
Signed-off-by: Sam Protsenko <semen.protsenko@linaro.org>