notes.h: declare bit field as unsigned to silence compiler complaints

The IRIX MIPSPro compiler complains like this:

   cc-1107 c99: WARNING File = notes.h, Line = 215
     A signed bit field has a length of 1 bit.

           int suppress_default_notes:1;
               ^

'unsigned' is what was intended, so lets make it so.

Signed-off-by: Brandon Casey <casey@nrlssc.navy.mil>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/notes.h b/notes.h
index ee65bd1..9f59277 100644
--- a/notes.h
+++ b/notes.h
@@ -212,7 +212,7 @@
 struct string_list;
 
 struct display_notes_opt {
-	int suppress_default_notes:1;
+	unsigned int suppress_default_notes:1;
 	struct string_list *extra_notes_refs;
 };