NFSv4.1: fix break condition in pnfs_find_lseg

The break condition to skip out of the loop got broken when cmp_layout
was change.  Essentially, we want to stop looking once we know no layout
on the remainder of the list can match the first byte of the looked-up
range.

Reported-by: Peng Tao <peng_tao@emc.com>
Signed-off-by: Benny Halevy <benny@tonian.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>