Fix warning about unsequenced modification of variable

Variable t was read and modified without interleaving sequence points,
technically undefined behavior. Report by Clang's -Wunsequenced

src/shapes.c

@@ -683,5 +683,5 @@ Rectangle GetCollisionRec(Rectangle rec1, Rectangle rec2)
 static float EaseCubicInOut(float t, float b, float c, float d) 
 { 
     if ((t/=d/2) < 1) return (c/2*t*t*t + b);
-    return (c/2*((t-=2)*t*t + 2) + b);
-}
+    return (c/2*((t-2)*t*t + 2) + b);
+}