s390/mm: improve debugfs ptdump markers walking

This allows to print multiple markers when they happened to have the
same value.

...
0x001bfffff0100000-0x001c000000000000       255M PMD I
---[ Kasan Shadow End ]---
---[ vmemmap Area ]---
0x001c000000000000-0x001c000002000000        32M PMD RW X
...
Reviewed-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

arch/s390/mm/dump_pagetables.c

@@ -100,7 +100,7 @@ static void note_page(struct seq_file *m, struct pg_state *st,
 		}
 		seq_printf(m, "%9lu%c ", delta, *unit);
 		print_prot(m, st->current_prot, st->level);
-		if (st->current_address >= st->marker[1].start_address) {
+		while (st->current_address >= st->marker[1].start_address) {
 			st->marker++;
 			seq_printf(m, "---[ %s ]---\n", st->marker->name);
 		}