Btrfs: fix arithmetic error in clone ioctl

Fix an arithmetic error that was breaking extents cloned via the clone
ioctl starting in the second half of a file.

Signed-off-by: Sage Weil <sage@newdream.net>
Signed-off-by: Chris Mason <chris.mason@oracle.com>
diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index a13fd55..a8577a7 100644
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -1105,8 +1105,7 @@
 					datao += off - key.offset;
 					datal -= off - key.offset;
 				}
-				if (key.offset + datao + datal + key.offset >
-				    off + len)
+				if (key.offset + datao + datal > off + len)
 					datal = off + len - key.offset - datao;
 				/* disko == 0 means it's a hole */
 				if (!disko)