`expect_fun_call` does not trigger to references

[TethysSvensson]

The lint expect_fun_call does not trigger for references. This code should output the warning for both foo and bar, but it only outputs it for bar.

fn foo(x: &Option<[u8; 32]>) -> [u8; 32] {
    x.expect(&format!("Call to format: {:?}", x))
}

fn bar(x: Option<[u8; 32]>) -> [u8; 32] {
    x.expect(&format!("Call to format: {:?}", x))
}

fn main() {
    foo(&Some([0; 32]));
    bar(Some([0; 32]));
}

As a fun side-note, this was found by profiling our code and noticing that 50% of it was spent inside a call to format!().