NFSv4: Fix locking in pnfs_generic_recover_commit_reqs

NFSv4: Fix locking in pnfs_generic_recover_commit_reqs

BugLink: https://bugs.launchpad.net/bugs/1835972
commit d0fbb1d8a194c0ec0180c1d073ad709e45503a43 upstream.

The use of the inode->i_lock was converted to a mutex, but we forgot
to remove the old inode unlock/lock() pair that allowed the layout
segment to be put inside the loop.

Reported-by: Jia-Ju Bai <baijiaju1990@gmail.com>
Fixes: e824f99adaaf1 ("NFSv4: Use a mutex to protect the per-inode commit...")
Cc: stable@vger.kernel.org # v4.14+
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>