ref_soft: fix pointer-to-int casts

ref_soft/r_edge.c

@@ -1250,7 +1250,7 @@ void D_DrawflatSurfaces (void)
 
 		// make a stable color for each surface by taking the low
 		// bits of the msurface pointer
-		D_FlatFillSurface (s, (int)s->msurf & 0xFFFF);
+		D_FlatFillSurface (s, (uintptr_t)s->msurf & 0xFFFF);
 		D_DrawZSpans (s->spans);
 	}
 }