s390/tty: Fix a potential memory leak bug

The check for get_zeroed_page() leads to a direct return
and overlooked the memory leak caused by loop allocation.
Add a free helper to free spaces allocated by get_zeroed_page().

Signed-off-by: Haoxiang Li <[e-mail]>
Acked-by: Heiko Carstens <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Vasily Gorbik <[e-mail]>

drivers/s390/char/sclp_tty.c

···
 	.flush_buffer = sclp_tty_flush_buffer,
 };
 
+/* Release allocated pages. */
+static void __init __sclp_tty_free_pages(void)
+{
+	struct list_head *page, *p;
+
+	list_for_each_safe(page, p, &sclp_tty_pages) {
+		list_del(page);
+		free_page((unsigned long)page);
+	}
+}
+
 static int __init
 sclp_tty_init(void)
 {
···
 	for (i = 0; i < MAX_KMEM_PAGES; i++) {
 		page = (void *) get_zeroed_page(GFP_KERNEL | GFP_DMA);
 		if (page == NULL) {
+			__sclp_tty_free_pages();
 			tty_driver_kref_put(driver);
 			return -ENOMEM;
 		}