[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/jmr3927/common/prom.c b/arch/mips/jmr3927/common/prom.c
index 5d5838f..aa481b7 100644
--- a/arch/mips/jmr3927/common/prom.c
+++ b/arch/mips/jmr3927/common/prom.c
@@ -75,7 +75,6 @@
 	*cp = '\0';
 }
 
-unsigned long __init prom_free_prom_memory(void)
+void __init prom_free_prom_memory(void)
 {
-	return 0;
 }