Update MultiplyAdd

Author: JimBobSquarePants

src/ImageSharp/Common/Helpers/Vector256Utilities.cs

@@ -146,7 +146,7 @@ public static Vector256<float> MultiplyAdd(
     {
         if (Fma.IsSupported)
         {
-            return Fma.MultiplyAdd(vm1, vm0, va);
+            return Fma.MultiplyAdd(vm0, vm1, va);
         }
 
         if (Avx.IsSupported)

src/ImageSharp/Common/Helpers/Vector512Utilities.cs

@@ -145,7 +145,15 @@ public static Vector512<float> RoundToNearestInteger(Vector512<float> vector)
     public static Vector512<float> MultiplyAdd(
         Vector512<float> va,
         Vector512<float> vm0,
-        Vector512<float> vm1) => va + (vm0 * vm1);
+        Vector512<float> vm1)
+    {
+        if (Avx512F.IsSupported)
+        {
+            return Avx512F.FusedMultiplyAdd(vm0, vm1, va);
+        }
+
+        return va + (vm0 * vm1);
+    }
 
     [DoesNotReturn]
     private static void ThrowUnreachableException() => throw new UnreachableException();