libobs/graphics: Remove redundant variable assignment

libobs/graphics/matrix4.c

@@ -231,7 +231,7 @@ void matrix4_scale_i(struct matrix4 *dst, const struct vec3 *v,
 
 bool matrix4_inv(struct matrix4 *dst, const struct matrix4 *m)
 {
-	struct vec4 *dstv = (struct vec4 *)dst;
+	struct vec4 *dstv;
 	float det;
 	float m3x3[9];
 	int   i, j, sign;