modify the error message- CR Comments

src/test/compile-fail/borrowck/borrowck-issue-14498.rs

@@ -27,7 +27,7 @@ fn indirect_write_to_imm_box() {
     let y: Box<_> = box &mut x;
     let p = &y;
     ***p = 2; //[ast]~ ERROR cannot assign to data in a `&` reference
-              //[mir]~^ ERROR cannot assign through `&`-reference `p`
+              //[mir]~^ ERROR cannot assign to data in a `&` reference
     drop(p);
 }
 

src/test/compile-fail/borrowck/borrowck-overloaded-index-ref-index.rs

@@ -70,5 +70,5 @@ fn main() {
     };
     s[2] = 20;
     //[ast]~^ ERROR cannot assign to immutable indexed content
-    //[mir]~^^ ERROR cannot assign through immutable item
+    //[mir]~^^ ERROR cannot assign to immutable item
 }

src/test/ui/nll/issue-47388.stderr

@@ -1,10 +1,10 @@
-error[E0594]: cannot assign through `&`-reference `fancy_ref`
+error[E0594]: cannot assign to data in a `&` reference
   --> $DIR/issue-47388.rs:18:5
    |
 LL |     let fancy_ref = &(&mut fancy);
    |                     ------------- help: consider changing this to be a mutable reference: `&mut`
 LL |     fancy_ref.num = 6; //~ ERROR E0594
-   |     ^^^^^^^^^^^^^^^^^ cannot assign through `&`-reference
+   |     ^^^^^^^^^^^^^^^^^ `fancy_ref` is a `&` reference, so the data it refers to cannot be written
 
 error: aborting due to previous error