obs-d3d11: include float.h for FLT_MAX

gcc expects this header to be included

libobs-d3d11/d3d11-samplerstate.cpp

@@ -16,6 +16,7 @@
 ******************************************************************************/
 
 #include <graphics/vec4.h>
+#include <float.h>
 
 #include "d3d11-subsystem.hpp"