f2fs: fix to avoid uninit-value access in f2fs_sanity_check_node_footer

In the Linux kernel, the following vulnerability has been resolved:

f2fs: fix to avoid uninit-value access in f2fs_sanity_check_node_footer

syzbot reported a f2fs bug as below:

BUG: KMSAN: uninit-value in f2fs_sanity_check_node_footer+0x374/0xa20 fs/f2fs/node.c:1520
f2fs_sanity_check_node_footer+0x374/0xa20 fs/f2fs/node.c:1520
f2fs_finish_read_bio+0xe1e/0x1d60 fs/f2fs/data.c:177
f2fs_read_end_io+0x6ab/0x2220 fs/f2fs/data.c:-1
bio_endio+0x1006/0x1160 block/bio.c:1792
submit_bio_noacct+0x533/0x2960 block/blk-core.c:891
submit_bio+0x57a/0x620 block/blk-core.c:926
blk_crypto_submit_bio include/linux/blk-crypto.h:203 [inline]
f2fs_submit_read_bio+0x12c/0x360 fs/f2fs/data.c:557
f2fs_submit_page_bio+0xee2/0x1450 fs/f2fs/data.c:775
read_node_folio+0x384/0x4b0 fs/f2fs/node.c:1481
__get_node_folio+0x5db/0x15d0 fs/f2fs/node.c:1576
f2fs_get_inode_folio+0x40/0x50 fs/f2fs/node.c:1623
do_read_inode fs/f2fs/inode.c:425 [inline]
f2fs_iget+0x1209/0x9380 fs/f2fs/inode.c:596
f2fs_fill_super+0x8f5a/0xb2e0 fs/f2fs/super.c:5184
get_tree_bdev_flags+0x6e6/0x920 fs/super.c:1694
get_tree_bdev+0x38/0x50 fs/super.c:1717
f2fs_get_tree+0x35/0x40 fs/f2fs/super.c:5436
vfs_get_tree+0xb3/0x5d0 fs/super.c:1754
fc_mount fs/namespace.c:1193 [inline]
do_new_mount_fc fs/namespace.c:3763 [inline]
do_new_mount+0x885/0x1dd0 fs/namespace.c:3839
path_mount+0x7a2/0x20b0 fs/namespace.c:4159
do_mount fs/namespace.c:4172 [inline]
__do_sys_mount fs/namespace.c:4361 [inline]
__se_sys_mount+0x704/0x7f0 fs/namespace.c:4338
__x64_sys_mount+0xe4/0x150 fs/namespace.c:4338
x64_sys_call+0x39f0/0x3ea0 arch/x86/include/generated/asm/syscalls_64.h:166
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x134/0xf80 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

The root cause is: in f2fs_finish_read_bio(), we may access uninit data
in folio if we failed to read the data from device into folio, let's add
a check condition to avoid such issue.