Use !0 instead of usize::MAX

We could use core::usize::MAX, but that is deprecated.

Signed-off-by: Joe Richey <joerichey@google.com>

src/rdrand.rs

@@ -50,8 +50,8 @@ compile_error!(
 // Fails with probability < 2^(-90) on 32-bit systems
 #[target_feature(enable = "rdrand")]
 unsafe fn self_test() -> bool {
-    // On AMD, RDRAND returns usize::MAX on failure, count it as a collision.
-    let mut prev = usize::MAX;
+    // On AMD, RDRAND returns 0xFF...FF on failure, count it as a collision.
+    let mut prev = !0; // TODO(MSRV 1.43): Move to usize::MAX
     let mut fails = 0;
     for _ in 0..8 {
         match rdrand() {