km/common: remove saveenv from do_checkboardidhwkey

This is unneeded here because we save the environment when
the board boots the first time. At this time we have set
the values already.

Signed-off-by: Holger Brunck <holger.brunck@keymile.com>
Signed-off-by: Valentin Longchamp <valentin.longchamp@keymile.com>
cc: Heiko Schocher <hs@denx.de>
cc: Wolfgang Denk <wd@denx.de>