[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/lasat/prom.c b/arch/mips/lasat/prom.c
index 88c7ab8..d47692f 100644
--- a/arch/mips/lasat/prom.c
+++ b/arch/mips/lasat/prom.c
@@ -132,9 +132,8 @@
 	add_memory_region(0, lasat_board_info.li_memsize, BOOT_MEM_RAM);
 }
 
-unsigned long __init prom_free_prom_memory(void)
+void __init prom_free_prom_memory(void)
 {
-	return 0;
 }
 
 const char *get_system_type(void)