glx: Log the filename of the drm device if we fail to open it

Helps point the user to the specific device that's having issues, since
you're increasingly likely to have more than one.

Gitlab: https://gitlab.freedesktop.org/mesa/mesa/issues/107
Reviewed-by: Eric Anholt <eric@anholt.net>
diff --git a/src/glx/dri2_glx.c b/src/glx/dri2_glx.c
index bed25bb..d2a9c88 100644
--- a/src/glx/dri2_glx.c
+++ b/src/glx/dri2_glx.c
@@ -1244,7 +1244,7 @@
 
    psc->fd = loader_open_device(deviceName);
    if (psc->fd < 0) {
-      ErrorMessageF("failed to open drm device: %s\n", strerror(errno));
+      ErrorMessageF("failed to open %s: %s\n", deviceName, strerror(errno));
       goto handle_error;
    }