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>

Author: Trott

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){
-lethas_N,has_r,has_p;
-if(has_N=(options.N!==undefined)){
+consthas_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)){
+consthas_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)){
+consthas_p=options.p!==undefined;
+if(has_p){
 p=options.p;
 validateUint32(p,'p');
 }