floppy: Remove unused CROSS_64KB() macro from arch/ code

floppy: Remove unused CROSS_64KB() macro from arch/ code

Since the commit 3d86739c6343 ("floppy: always use the track buffer")
the CROSS_64KB() is not used by the driver, remove the leftovers.

Acked-by: Helge Deller <deller@gmx.de> #parisc
Acked-by: Geert Uytterhoeven <geert@linux-m68k.org> # m68k
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20250825163545.39303-2-andriy.shevchenko@linux.intel.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>