x/crypto/chacha20: fix typo in benchmark

Change-Id: I003c389585a42089fc9cc595d1f5f1027cd482f2
Reviewed-on: https://go-review.googlesource.com/c/crypto/+/272306
Trust: Roland Shoemaker <[email protected]>
Run-TryBot: Roland Shoemaker <[email protected]>
TryBot-Result: Go Bot <[email protected]>
Reviewed-by: Katie Hockman <[email protected]>

Author: rolandshoemaker

chacha20/chacha_test.go

@@ -238,7 +238,7 @@ func BenchmarkChaCha20(b *testing.B) {
 		benchmarkChaCha20(b, 10, 25)
 	})
 	b.Run("4096", func(b *testing.B) {
-		benchmarkChaCha20(b, 256, 1)
+		benchmarkChaCha20(b, 4096, 1)
 	})
 	b.Run("100x40", func(b *testing.B) {
 		benchmarkChaCha20(b, 100, 40)