crypto: revise variables for const use instead of let

This prepares the code for enabling the no-cond-assign rule.

PR-URL: #41614
Reviewed-By: Tobias Nießen <tniessen@tnie.de>
Reviewed-By: Anna Henningsen <anna@addaleax.net>

lib/internal/crypto/scrypt.js

@@ -98,8 +98,8 @@ function check(password, salt, keylen, options) {
 
   let { N, r, p, maxmem } = defaults;
   if (options && options !== defaults) {
-    let has_N, has_r, has_p;
-    if (has_N = (options.N !== undefined)) {
+    const has_N = options.N !== undefined;
+    if (has_N) {
       N = options.N;
       validateUint32(N, 'N');
     }
@@ -108,7 +108,8 @@ function check(password, salt, keylen, options) {
       N = options.cost;
       validateUint32(N, 'cost');
     }
-    if (has_r = (options.r !== undefined)) {
+    const has_r = (options.r !== undefined);
+    if (has_r) {
       r = options.r;
       validateUint32(r, 'r');
     }
@@ -117,7 +118,8 @@ function check(password, salt, keylen, options) {
       r = options.blockSize;
       validateUint32(r, 'blockSize');
     }
-    if (has_p = (options.p !== undefined)) {
+    const has_p = options.p !== undefined;
+    if (has_p) {
       p = options.p;
       validateUint32(p, 'p');
     }