libnilfs: fix error code when nilfs_open failed to find nilfs

In the current implementation, if nilfs_open() fails to retrieve an
existing nilfs mount from the mount table, it returns an error with
errno = ENOENT, resulting in inappropriate error messages, such as the
following:

$ lscp /dev/sdb1
lscp: cannot open NILFS on /dev/sdb1: No such file or directory

Fix this issue by changing the error code set in errno to ENXIO.

Signed-off-by: Ryusuke Konishi <konishi.ryusuke@gmail.com>

Author: konis

lib/nilfs.c

@@ -241,7 +241,7 @@ static int nilfs_find_fs(struct nilfs *nilfs, const char *dev, const char *dir,
 		}
 	}
 	if (ret < 0)
-		errno = ENOENT;
+		errno = ENXIO;
 
  failed_proc_mounts:
 	fclose(fp);