NFSv4.1: use pnfs_generic_pg_test directly by layout driver

Signed-off-by: Benny Halevy <bhalevy@panasas.com>
diff --git a/fs/nfs/nfs4filelayout.c b/fs/nfs/nfs4filelayout.c
index 24f0572..4269088 100644
--- a/fs/nfs/nfs4filelayout.c
+++ b/fs/nfs/nfs4filelayout.c
@@ -661,6 +661,9 @@
 	u64 p_stripe, r_stripe;
 	u32 stripe_unit;
 
+	if (!pnfs_generic_pg_test(pgio, prev, req))
+		return 0;
+
 	if (!pgio->pg_lseg)
 		return 1;
 	p_stripe = (u64)prev->wb_index << PAGE_CACHE_SHIFT;