[U-Boot] [PATCH] tools/kwbimage.c: fix build on m68k

[Angelo Dureghello]

Dear Lukasz,
> Hi Angelo,
> You aren't the first person who attempted to fix this.

i read the history of the fixes done on this file before posting,
and seen the issue was solved using a "switch / case" approach.

I was testing yesterday the kernel.org x86 toolchain for m68k,
(m68k/gcc-4.6.3-nolibc) and found this warning emitted building the
master branch,so i posted the patch since is possible the warning
is thrown only with this m68k toolchain.

So i don't want absolutely overlap ongoing jobs, if they are already
in chargeto anyone simply ignore the patch.

Best Regards,
Angelo Dureghello