xfs: clean up sign warnings in dir2 code

We are now consistently using unsigned char strings for names
so fix up the remaining warnings in the dir2 code to complete
the cleanup.

Signed-off-by: Dave Chinner <david@fromorbit.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
diff --git a/fs/xfs/xfs_dir2.c b/fs/xfs/xfs_dir2.c
index 3a8c6ba0..42520f0 100644
--- a/fs/xfs/xfs_dir2.c
+++ b/fs/xfs/xfs_dir2.c
@@ -44,7 +44,7 @@
 #include "xfs_vnodeops.h"
 #include "xfs_trace.h"
 
-struct xfs_name xfs_name_dotdot = {"..", 2};
+struct xfs_name xfs_name_dotdot = { (unsigned char *)"..", 2};
 
 /*
  * ASCII case-insensitive (ie. A-Z) support for directories that was