drm: drm_ut_debug_printk() isn't called with NULL anywmore

The DRM_LOG* macros where the only sites where drm_ut_debug_printk was
called with NULL arguments for prefix and function_name. Now that they
are gone, we can remove that case.
Signed-off-by: Damien Lespiau <damien.lespiau@intel.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>

drivers/gpu/drm/drm_stub.c

@@ -108,11 +108,7 @@ void drm_ut_debug_printk(const char *prefix,
 	vaf.fmt = format;
 	vaf.va = &args;
 
-	if (function_name)
-		printk(KERN_DEBUG "[%s:%s], %pV", prefix,
-		       function_name, &vaf);
-	else
-		printk(KERN_DEBUG "%pV", &vaf);
+	printk(KERN_DEBUG "[%s:%s], %pV", prefix, function_name, &vaf);
 
 	va_end(args);
 }