btrfs-progs: send: fix failure of fstests btrfs/038

btrfs-progs: send: fix failure of fstests btrfs/038

The following patch was imperfect, so xfstests btrfs/038 was failed.

  6d4fb3d  btrfs-progs: send: fix handling of multiple snapshots (-p option)

[before]
| # ./check btrfs/038
| FSTYP         -- btrfs
| PLATFORM      -- Linux/x86_64 luna 4.9.0-rc5
| MKFS_OPTIONS  -- /dev/sdb3
| MOUNT_OPTIONS -- /dev/sdb3 /test6
|
| btrfs/038 1s ... [failed, exit status 1] - output mismatch (see /For_RT/xfstests2/results//btrfs/038.out.bad)
|     --- tests/btrfs/038.out     2015-08-04 16:09:38.000000000 +0900
|     +++ /For_RT/xfstests2/results//btrfs/038.out.bad    2016-11-15 13:39:48.589435290 +0900
|     @@ -7,3 +7,5 @@
|      XXX Bytes, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
|      wrote 10000/10000 bytes at offset 300000
|      XXX Bytes, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
|     +failed: '/usr/local/bin/btrfs send -p /test6/mysnap1 -c /test6/clones_snap /test6/mysnap2 -f /tmp/tmp.aLpvAC7lsx/2.snap'
|     +(see /For_RT/xfstests2/results//btrfs/038.full for details)
|     ...
|     (Run 'diff -u tests/btrfs/038.out /For_RT/xfstests2/results//btrfs/038.out.bad'  to see the entire diff)
| Ran: btrfs/038
| Failures: btrfs/038

[after]
| # ./check btrfs/038
| FSTYP         -- btrfs
| PLATFORM      -- Linux/x86_64 luna 4.9.0-rc5
| MKFS_OPTIONS  -- /dev/sdb3
| MOUNT_OPTIONS -- /dev/sdb3 /test6
|
| btrfs/038 1s ... 1s
| Ran: btrfs/038
| Passed all 1 tests

Signed-off-by: Tsutomu Itoh <t-itoh@jp.fujitsu.com>
[ Verified that this fixes both btrfs/038 and btrfs/117 ]
Tested-by: Omar Sandoval <osandov@fb.com>
Signed-off-by: David Sterba <dsterba@suse.com>