[GFS2] Fix log block mapper

A missing offset in the calculation.

Signed-off-by: Steven Whitehouse <swhiteho@redhat.com>
diff --git a/fs/gfs2/log.c b/fs/gfs2/log.c
index 69a583e..9164525 100644
--- a/fs/gfs2/log.c
+++ b/fs/gfs2/log.c
@@ -343,7 +343,7 @@
 
 	list_for_each_entry(je, &sdp->sd_jdesc->extent_list, extent_list) {
 		if (lbn >= je->lblock && lbn < je->lblock + je->blocks)
-			return je->dblock + lbn;
+			return je->dblock + lbn - je->lblock;
 	}
 
 	return -1;