m68k: fix ColdFire mmu init compile warning

Compiling for MMU enabled ColdFire targets gives a warning:

CC arch/m68k/mm/mcfmmu.o
arch/m68k/mm/mcfmmu.c: In function ‘paging_init’:
arch/m68k/mm/mcfmmu.c:42:17: warning: unused variable ‘zone’ [-Wunused-variable]
enum zone_type zone;
^~~~

This was caused by changes in commit fa3354e4ea39 ("mm: free_area_init:
use maximal zone PFNs rather than zone sizes") leaving around a now
unused variable declaration. Remove the unused variable.

Signed-off-by: Greg Ungerer <[e-mail]>

arch/m68k/mm/mcfmmu.c

···
 	unsigned long address, size;
 	unsigned long next_pgtable, bootmem_end;
 	unsigned long max_zone_pfn[MAX_NR_ZONES] = { 0 };
-	enum zone_type zone;
 	int i;
 
 	empty_zero_page = (void *) memblock_alloc(PAGE_SIZE, PAGE_SIZE);