m68k: mm: Remove superfluous memblock_alloc*() casts

The return type of memblock_alloc*() is a void pointer, so there is no
need to cast it to "void *" or some other pointer type, before assigning
it to a pointer variable.

Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Reviewed-by: Mike Rapoport <rppt@linux.ibm.com>
Acked-by: Greg Ungerer <gerg@linux-m68k.org>
Link: https://lore.kernel.org/r/20200826130444.25618-1-geert@linux-m68k.org