i965/disasm: Mark format() as being printf-style.

This allows us to get warnings from GCC when we mess up the format
strings.

Signed-off-by: Chris Forbes <chrisf@ijw.co.nz>
Reviewed-by: Matt Turner <mattst88@gmail.com>

src/mesa/drivers/dri/i965/brw_disasm.c

@@ -596,6 +596,9 @@ string(FILE *file, const char *string)
    return 0;
 }
 
+static int
+format(FILE *f, const char *format, ...) PRINTFLIKE(2, 3);
+
 static int
 format(FILE *f, const char *format, ...)
 {