winex11: Multiply the error tolerance by the table caused error magnification.

dlls/gdi32/tests/dc.c

@@ -765,7 +765,7 @@ static void test_gamma(void)
     ramp[0][0] = 0;
     for (i = 1; i < 256; i++) ramp[0][i] = ramp[0][i - 1] + 512;
     ret = SetDeviceGammaRamp(hdc, &ramp);
-    todo_wine ok(ret, "SetDeviceGammaRamp failed\n");
+    ok(ret, "SetDeviceGammaRamp failed\n");
 
     /* cleanup: set old ramp again */
     ret = SetDeviceGammaRamp(hdc, &oldramp);

dlls/winex11.drv/xvidmode.c

@@ -335,7 +335,7 @@ static BOOL ComputeGammaFromRamp(WORD ramp[256], float *gamma)
     return FALSE;
   }
   /* check that the gamma is reasonably uniform across the ramp */
-  if (g_max - g_min > 0.1) {
+  if (g_max - g_min > 12.8) {
     ERR("ramp not uniform (max=%f, min=%f, avg=%f), rejected\n", g_max, g_min, g_avg);
     return FALSE;
   }