m68k: Fix indentation by 2 or 5 spaces in <asm/page_mm.h>

Indentation should use TABs, not spaces.
Fix whitespace in reindented code while at it.

Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Link: https://lore.kernel.org/r/2819709eee2be69c93497d4e97413bd0e05a9268.1696602993.git.geert@linux-m68k.org