[MIPS] prom_free_prom_memory cleanup

Current prom_free_prom_memory() implementations are almost same as
free_init_pages(), or no-op.  Make free_init_pages() extern (again)
and make prom_free_prom_memory() use it.

Signed-off-by: Atsushi Nemoto <anemo@mba.ocn.ne.jp>
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
diff --git a/arch/mips/cobalt/setup.c b/arch/mips/cobalt/setup.c
index e8f0f20..a4b69b5 100644
--- a/arch/mips/cobalt/setup.c
+++ b/arch/mips/cobalt/setup.c
@@ -204,8 +204,7 @@
 	add_memory_region(0x0, memsz, BOOT_MEM_RAM);
 }
 
-unsigned long __init prom_free_prom_memory(void)
+void __init prom_free_prom_memory(void)
 {
 	/* Nothing to do! */
-	return 0;
 }