f2fs: fix to unlock page correctly in error path of is_alive()

As Pavel Machek reported in below link [1]:

After commit 77900c45 ("f2fs: fix to do sanity check in is_alive()"),
node page should be unlock via calling f2fs_put_page() in the error path
of is_alive(), otherwise, f2fs may hang when it tries to lock the node
page, fix it.

[1] https://lore.kernel.org/stable/20220124203637.GA19321@duo.ucw.cz/



Fixes: 77900c45 ("f2fs: fix to do sanity check in is_alive()")
Cc: <stable@vger.kernel.org>
Reported-by: Pavel Machek <pavel@denx.de>
Signed-off-by: Pavel Machek <pavel@denx.de>
Signed-off-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>