syzbot reported a bug which could cause shift-out-of-bounds issue,
fix it.

Call Trace:
 __dump_stack lib/dump_stack.c:79 [inline]
 dump_stack+0x107/0x163 lib/dump_stack.c:120
 ubsan_epilogue+0xb/0x5a lib/ubsan.c:148
 __ubsan_handle_shift_out_of_bounds.cold+0xb1/0x181 lib/ubsan.c:395
 sanity_check_raw_super fs/f2fs/super.c:2812 [inline]
 read_raw_super_block fs/f2fs/super.c:3267 [inline]
 f2fs_fill_super.cold+0x16c9/0x16f6 fs/f2fs/super.c:3519
 mount_bdev+0x34d/0x410 fs/super.c:1366
 legacy_get_tree+0x105/0x220 fs/fs_context.c:592
 vfs_get_tree+0x89/0x2f0 fs/super.c:1496
 do_new_mount fs/namespace.c:2896 [inline]
 path_mount+0x12ae/0x1e70 fs/namespace.c:3227
 do_mount fs/namespace.c:3240 [inline]
 __do_sys_mount fs/namespace.c:3448 [inline]
 __se_sys_mount fs/namespace.c:3425 [inline]
 __x64_sys_mount+0x27f/0x300 fs/namespace.c:3425
 do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported-by: syzbot+ca9a785f8ac472085994@syzkaller.appspotmail.com
Signed-off-by: NAnant Thazhemadam <anant.thazhemadam@gmail.com>
Signed-off-by: NChao Yu <yuchao0@huawei.com>
Signed-off-by: NJaegeuk Kim <jaegeuk@kernel.org>