libobs: fix building modules once installed

sse-intrin.h is a required header now, but the implicit path
breaks building addons once the headers are installed.

Fix this by making the path explicit.

libobs/media-io/format-conversion.c

@@ -17,7 +17,7 @@
 
 #include "format-conversion.h"
 
-#include <util/sse-intrin.h>
+#include "../util/sse-intrin.h"
 
 /* ...surprisingly, if I don't use a macro to force inlining, it causes the
  * CPU usage to boost by a tremendous amount in debug builds. */