ARM: kirkwood: ib62x0: fix size of u-boot environment partition

Commit 148c274e ("ARM: kirkwood: ib62x0: add u-boot environment
partition") split the "u-boot" partition into "u-boot" and "u-boot
environment".  However, instead of the size of the environment, an offset
was given, resulting in overlapping partitions.

Signed-off-by: Simon Baatz <gmbnomis@gmail.com>
Fixes: 148c274e ("ARM: kirkwood: ib62x0: add u-boot environment partition")
Cc: Jason Cooper <jason@lakedaemon.net>
Cc: Andrew Lunn <andrew@lunn.ch>
Cc: Gregory Clement <gregory.clement@free-electrons.com>
Cc: Sebastian Hesselbarth <sebastian.hesselbarth@gmail.com>
Cc: Luka Perkov <luka@openwrt.org>
Cc: stable@vger.kernel.org # 3.13+
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Gregory CLEMENT <gregory.clement@free-electrons.com>