dri: Fix the logger error message handling.

dri: Fix the logger error message handling.

Since the loader changes, there has been a compiler warning that the
prototype didn't match.  It turns out that if a loader error message was
ever thrown, you'd segfault because of trying to use the warning level as
a format string.

Reviewed-by: Keith Packard <keithp@keithp.com>
Tested-by: Keith Packard <keithp@keithp.com>
Reviewed-by: Kristian Høgsberg <krh@bitplanet.net>