E0396 needs to be updated to new format

[sophiajt]

From: src/test/compile-fail/E0396.rs

E0396 needs a span_label, updating it from:

error[E0396]: raw pointers cannot be dereferenced in constants
  --> src/test/compile-fail/E0396.rs:13:28
   |
13 | const VALUE: u8 = unsafe { *REG_ADDR }; //~ ERROR E0396
   |                            ^^^^^^^^^

To:

error[E0396]: raw pointers cannot be dereferenced in constants
  --> src/test/compile-fail/E0396.rs:13:28
   |
13 | const VALUE: u8 = unsafe { *REG_ADDR }; //~ ERROR E0396
   |                            ^^^^^^^^^ dereference of raw pointer in constant

[clementmiao]

I can take this!