m68knommu: fix build when CPU is not coldfire

Commit dd1cb3a7 [merge MMU and non-MMU
versions of mm/init.c] unified mm/init.c for both MMU and non-MMU m68k
platforms. However, it broke when we build a non-MMU M68K Classic CPU kernel.

This fix builds a section that came from the MMU version only when we are
building a MMU kernel.
Signed-off-by: NThadeu Lima de Souza Cascardo <cascardo@holoscopio.com>
Signed-off-by: NGreg Ungerer <gerg@uclinux.org>

arch/m68k/mm/init.c

@@ -188,7 +188,7 @@ void __init mem_init(void)
 		}
 	}
 
-#if !defined(CONFIG_SUN3) && !defined(CONFIG_COLDFIRE)
+#if defined(CONFIG_MMU) && !defined(CONFIG_SUN3) && !defined(CONFIG_COLDFIRE)
 	/* insert pointer tables allocated so far into the tablelist */
 	init_pointer_table((unsigned long)kernel_pg_dir);
 	for (i = 0; i < PTRS_PER_PGD; i++) {