NFS/flexfile: Simplify nfs4_ff_layout_select_ds_stateid()

Pass in a pointer to the mirror rather than forcing another
array access.

Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
diff --git a/fs/nfs/flexfilelayout/flexfilelayout.h b/fs/nfs/flexfilelayout/flexfilelayout.h
index 99cfe2e8..2f36996 100644
--- a/fs/nfs/flexfilelayout/flexfilelayout.h
+++ b/fs/nfs/flexfilelayout/flexfilelayout.h
@@ -204,10 +204,9 @@
 		unsigned int maxnum);
 struct nfs_fh *
 nfs4_ff_layout_select_ds_fh(struct nfs4_ff_layout_mirror *mirror);
-int
-nfs4_ff_layout_select_ds_stateid(struct pnfs_layout_segment *lseg,
-				u32 mirror_idx,
-				nfs4_stateid *stateid);
+void
+nfs4_ff_layout_select_ds_stateid(const struct nfs4_ff_layout_mirror *mirror,
+		nfs4_stateid *stateid);
 
 struct nfs4_pnfs_ds *
 nfs4_ff_layout_prepare_ds(struct pnfs_layout_segment *lseg,