libceph: fix possible CONFIG_BLOCK build problem

This patch:
    15a0d7b libceph: record message data length
did not enclose some bio-specific code inside CONFIG_BLOCK as
it should have.  Fix that.

Signed-off-by: Alex Elder <elder@inktank.com>
Reviewed-by: Josh Durgin <josh.durgin@inktank.com>
diff --git a/net/ceph/messenger.c b/net/ceph/messenger.c
index a6fda95..994192b 100644
--- a/net/ceph/messenger.c
+++ b/net/ceph/messenger.c
@@ -817,7 +817,7 @@
 
 	return true;
 }
-#endif
+#endif /* CONFIG_BLOCK */
 
 /*
  * For a page array, a piece comes from the first page in the array
@@ -3011,6 +3011,7 @@
 }
 EXPORT_SYMBOL(ceph_msg_data_set_pagelist);
 
+#ifdef	CONFIG_BLOCK
 void ceph_msg_data_set_bio(struct ceph_msg *msg, struct bio *bio,
 		size_t length)
 {
@@ -3028,6 +3029,7 @@
 	msg->data_length = length;
 }
 EXPORT_SYMBOL(ceph_msg_data_set_bio);
+#endif	/* CONFIG_BLOCK */
 
 /*
  * construct a new message with given type, size