f2fs: Fix uninitialized return in f2fs_ioc_shutdown()

"ret" can be uninitialized on the success path when "in ==
F2FS_GOING_DOWN_FULLSYNC".

Fixes: 60b2b4ee2b ("f2fs: Fix deadlock in shutdown ioctl")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/file.c

@@ -1866,7 +1866,7 @@ static int f2fs_ioc_shutdown(struct file *filp, unsigned long arg)
 	struct f2fs_sb_info *sbi = F2FS_I_SB(inode);
 	struct super_block *sb = sbi->sb;
 	__u32 in;
-	int ret;
+	int ret = 0;
 
 	if (!capable(CAP_SYS_ADMIN))
 		return -EPERM;