[S390] topology: fix alloc_masks annotation

Fix this warning:
WARNING: vmlinux.o(.text+0x199b6): Section mismatch in reference from
the function alloc_masks() to the function .init.text:__alloc_bootmem()
Signed-off-by: NSebastian Ott <sebott@linux.vnet.ibm.com>
Signed-off-by: NMartin Schwidefsky <schwidefsky@de.ibm.com>

arch/s390/kernel/topology.c

@@ -299,8 +299,8 @@ static int __init init_topology_update(void)
 }
 __initcall(init_topology_update);
 
-static void alloc_masks(struct sysinfo_15_1_x *info, struct mask_info *mask,
-			int offset)
+static void __init alloc_masks(struct sysinfo_15_1_x *info,
+			       struct mask_info *mask, int offset)
 {
 	int i, nr_masks;