ceph: make ceph_msg_new return NULL on failure; clean up, fix callers

Returning ERR_PTR(-ENOMEM) is useless extra work.  Return NULL on failure
instead, and fix up the callers (about half of which were wrong anyway).

Signed-off-by: Sage Weil <sage@newdream.net>
diff --git a/fs/ceph/caps.c b/fs/ceph/caps.c
index 51fd39d..8755e2d 100644
--- a/fs/ceph/caps.c
+++ b/fs/ceph/caps.c
@@ -939,8 +939,8 @@
 	     xattr_version, xattrs_buf ? (int)xattrs_buf->vec.iov_len : 0);
 
 	msg = ceph_msg_new(CEPH_MSG_CLIENT_CAPS, sizeof(*fc), 0, 0, NULL);
-	if (IS_ERR(msg))
-		return PTR_ERR(msg);
+	if (!msg)
+		return -ENOMEM;
 
 	msg->hdr.tid = cpu_to_le64(flush_tid);