As of commit 5df1abdbd37af2ae317a1c5b5944173284dc55d6 ('m68k/amiga: Fix
"debug=mem"'), "debug=mem" no longer uses amiga_chip_alloc_res(), so we
can remove the hack to prefer memory at the safe end.
This allows to simplify the code and make amiga_chip_alloc() just call
amiga_chip_alloc_res() internally.
Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>