NFSv4/pnfs: The layout barrier indicate a minimal value for the seqid

The intention of the layout barrier is to ensure that we do not update
the layout to match an older value than the current expectation. Fix the
test in pnfs_layout_stateid_blocked() to reflect that it is legal for
the seqid of the stateid to match that of the barrier.

Fixes: aa95edf3

 ("NFSv4/pnfs: Fix the layout barrier update")
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>