NFSv4.1/flexfiles: Fix incorrect usage of pnfs_generic_mark_devid_invalid()

Unlike the files layout, flexfiles does not test for the NFS_DEVICEID_INVALID
flag. Instead it relies on NFS_DEVICEID_UNAVAILABLE.
Fix is to replace with nfs4_mark_deviceid_unavailable().

Signed-off-by: Trond Myklebust <[e-mail]>

fs/nfs/flexfilelayout/flexfilelayoutdev.c

···
 			__func__, mirror_idx);
 		if (mirror && mirror->mirror_ds) {
 			devid = &mirror->mirror_ds->id_node;
-			pnfs_generic_mark_devid_invalid(devid);
+			nfs4_mark_deviceid_unavailable(devid);
 		}
 		goto out;
 	}
···
 			__func__, ds_idx);
 		if (mirror && mirror->mirror_ds) {
 			devid = &mirror->mirror_ds->id_node;
-			pnfs_generic_mark_devid_invalid(devid);
+			nfs4_mark_deviceid_unavailable(devid);
 		}
 		goto out;
 	}