nfs: rename pgio header ds_idx to ds_commit_idx

'ds_commit_idx' is a better name - it is used to select the right
commit bucket for pnfs.

Signed-off-by: Weston Andros Adamson <dros@primarydata.com>
diff --git a/fs/nfs/filelayout/filelayout.c b/fs/nfs/filelayout/filelayout.c
index 2af32fc..520cbc5 100644
--- a/fs/nfs/filelayout/filelayout.c
+++ b/fs/nfs/filelayout/filelayout.c
@@ -492,7 +492,7 @@
 	/* No multipath support. Use first DS */
 	atomic_inc(&ds->ds_clp->cl_count);
 	hdr->ds_clp = ds->ds_clp;
-	hdr->ds_idx = idx;
+	hdr->ds_commit_idx = idx;
 	fh = nfs4_fl_select_ds_fh(lseg, j);
 	if (fh)
 		hdr->args.fh = fh;
@@ -536,7 +536,7 @@
 	hdr->pgio_done_cb = filelayout_write_done_cb;
 	atomic_inc(&ds->ds_clp->cl_count);
 	hdr->ds_clp = ds->ds_clp;
-	hdr->ds_idx = idx;
+	hdr->ds_commit_idx = idx;
 	fh = nfs4_fl_select_ds_fh(lseg, j);
 	if (fh)
 		hdr->args.fh = fh;