ceph: check return value for start_request in writepages

Since we pass the nofail arg, we should never get an error; BUG if we do.
(And fix the function to not return an error if __map_request fails.)

Signed-off-by: Sage Weil <sage@newdream.net>
diff --git a/fs/ceph/addr.c b/fs/ceph/addr.c
index 5496726..33da49d 100644
--- a/fs/ceph/addr.c
+++ b/fs/ceph/addr.c
@@ -848,7 +848,8 @@
 		op->payload_len = cpu_to_le32(len);
 		req->r_request->hdr.data_len = cpu_to_le32(len);
 
-		ceph_osdc_start_request(&fsc->client->osdc, req, true);
+		rc = ceph_osdc_start_request(&fsc->client->osdc, req, true);
+		BUG_ON(rc);
 		req = NULL;
 
 		/* continue? */