crypto/rand: replace shift with constant

It was mentioned after CL 463993 was merged that it
is uncommon to use shifts for numbers other than
powers of ten. Replace the shift with a base 10 constant.

Change-Id: I11c90128740109a59add40ed7b680f7bcc9715ad
Reviewed-on: https://go-review.googlesource.com/c/go/+/465275
Auto-Submit: Johan Brandhorst-Satzkorn <[email protected]>
Run-TryBot: Johan Brandhorst-Satzkorn <[email protected]>
Reviewed-by: Dmitri Shuralyov <[email protected]>
Reviewed-by: Brad Fitzpatrick <[email protected]>
Auto-Submit: Brad Fitzpatrick <[email protected]>
Reviewed-by: David Chase <[email protected]>
TryBot-Result: Gopher Robot <[email protected]>

Author: johanbrandhorst

src/crypto/rand/rand_js.go

@@ -10,7 +10,7 @@ import "syscall/js"
 
 // The maximum buffer size for crypto.getRandomValues is 65536 bytes.
 // https://developer.mozilla.org/en-US/docs/Web/API/Crypto/getRandomValues#exceptions
-const maxGetRandomRead = 1 << 16
+const maxGetRandomRead = 64 << 10
 
 var batchedGetRandom func([]byte) error