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 <haoxiang_li2024@163.com>
Acked-by: Heiko Carstens <hca@linux.ibm.com>
Link: https://lore.kernel.org/r/20250218034104.2436469-1-haoxiang_li2024@163.com


Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>