nfsd: Fix a file leak on nfsd4_layout_setlease failure

If nfsd4_layout_setlease fails, nfsd will not put ls->ls_file.

Fix commit c5c707f9 "nfsd: implement pNFS layout recalls".

Signed-off-by: Kinglong Mee <kinglongmee@gmail.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>