m68k: mm: Fix systems with memory at end of 32-bit address space

The calculation of end addresses of memory chunks overflowed to 0 when
a memory chunk is located at the end of 32-bit address space.
This is the case for the HP300 architecture.

Link: https://lore.kernel.org/linux-m68k/CACz-3rhUo5pgNwdWHaPWmz+30Qo9xCg70wNxdf7o5x-6tXq8QQ@mail.gmail.com/


Signed-off-by: Kars de Jong <jongk@linux-m68k.org>
Reviewed-by: Geert Uytterhoeven <geert@linux-m68k.org>
Link: https://lore.kernel.org/r/20230223112349.26675-1-jongk@linux-m68k.org


Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>