internal/chacha20: fix variable naming

Wrong variable naming was causing 'go vet' to fail. This change fixes that.

Change-Id: I71e1842ece098198773fb326a725b57fad02f82f
Reviewed-on: https://go-review.googlesource.com/c/crypto/+/181720
Run-TryBot: Lynn Boger <laboger@linux.vnet.ibm.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Lynn Boger <laboger@linux.vnet.ibm.com>

internal/chacha20/asm_ppc64le.s

@@ -135,7 +135,7 @@ TEXT ·chaCha20_ctr32_vmx(SB),NOSPLIT|NOFRAME,$0
 	MOVD inp+8(FP), INP
 	MOVD len+16(FP), LEN
 	MOVD key+24(FP), KEY
-	MOVD cnt+32(FP), CNT
+	MOVD counter+32(FP), CNT
 
 	MOVD $·consts(SB), CONSTS // point to consts addr
 

internal/chacha20/chacha_ppc64le.go

@@ -8,9 +8,10 @@ package chacha20
 
 import "encoding/binary"
 
-var haveAsm = true
-
-const bufSize = 256
+const (
+	bufSize = 256
+	haveAsm = true
+)
 
 //go:noescape
 func chaCha20_ctr32_vmx(out, inp *byte, len int, key *[8]uint32, counter *uint32)