Don't suggest a.mul_add(b, c) if parameters are not float

clippy::suboptimal_flops used to not check if the second parameter to f32/f64.mul_add() was float. Since the method is
only defined to take `Self` as paremters, the suggestion was wrong.

Fixes #11831

tests/ui/floating_point_mul_add.fixed

@@ -39,3 +39,21 @@ fn main() {
     // Cases where the lint shouldn't be applied
     let _ = (a * a + b * b).sqrt();
 }
+
+fn _issue11831() {
+    struct NotAFloat;
+
+    impl std::ops::Add<f64> for NotAFloat {
+        type Output = Self;
+
+        fn add(self, _: f64) -> Self {
+            NotAFloat
+        }
+    }
+
+    let a = NotAFloat;
+    let b = 1.0_f64;
+    let c = 1.0;
+
+    let _ = a + b * c;
+}

tests/ui/floating_point_mul_add.rs

@@ -39,3 +39,21 @@ fn main() {
     // Cases where the lint shouldn't be applied
     let _ = (a * a + b * b).sqrt();
 }
+
+fn _issue11831() {
+    struct NotAFloat;
+
+    impl std::ops::Add<f64> for NotAFloat {
+        type Output = Self;
+
+        fn add(self, _: f64) -> Self {
+            NotAFloat
+        }
+    }
+
+    let a = NotAFloat;
+    let b = 1.0_f64;
+    let c = 1.0;
+
+    let _ = a + b * c;
+}