ext4: Add missing unlock_new_inode() call in extent migration code

We need to unlock the new inode before iput.  This patch fixes the
following warning when calling chattr +e to migrate a file to use
extents.  It also fixes problems in when e4defrag attempts to
defragment an inode.

[  470.400044] ------------[ cut here ]------------
[  470.400065] WARNING: at fs/inode.c:1210 generic_delete_inode+0x65/0x16a()
[  470.400072] Hardware name: N/A
.....
...
[  470.400353] Pid: 4451, comm: chattr Not tainted 2.6.31-rc7-red-debug #4
[  470.400359] Call Trace:
[  470.400372]  [<ffffffff81037771>] warn_slowpath_common+0x77/0x8f
[  470.400385]  [<ffffffff81037798>] warn_slowpath_null+0xf/0x11
[  470.400395]  [<ffffffff810b7f28>] generic_delete_inode+0x65/0x16a
[  470.400405]  [<ffffffff810b8044>] generic_drop_inode+0x17/0x1bd
[  470.400413]  [<ffffffff810b7083>] iput+0x61/0x65
[  470.400455]  [<ffffffffa003b229>] ext4_ext_migrate+0x5eb/0x66a [ext4]
[  470.400492]  [<ffffffffa002b1f8>] ext4_ioctl+0x340/0x756 [ext4]
[  470.400507]  [<ffffffff810b1a91>] vfs_ioctl+0x1d/0x82
[  470.400517]  [<ffffffff810b1ff0>] do_vfs_ioctl+0x483/0x4c9
[  470.400527]  [<ffffffff81059c30>] ? trace_hardirqs_on+0xd/0xf
[  470.400537]  [<ffffffff810b2087>] sys_ioctl+0x51/0x74
[  470.400549]  [<ffffffff8100ba6b>] system_call_fastpath+0x16/0x1b
[  470.400557] ---[ end trace ab85723542352dac ]---

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>