Fix format not a string literal error with -Werror=format-security

A trivial fix for error: format not a string literal and no format
arguments with compiling with -Werror=format-security flags.

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>

src/mesa/drivers/dri/i965/brw_fs.cpp

@@ -100,7 +100,7 @@ fs_visitor::fail(const char *format, ...)
    this->fail_msg = msg;
 
    if (INTEL_DEBUG & DEBUG_WM) {
-      fprintf(stderr, msg);
+      fprintf(stderr, "%s",  msg);
    }
 }