linter: (1/2) enable errcheck (#5064)

## Description

partially cleanup in preparation for errcheck

i ignored a bunch of defer errors in tests but with the update to go 1.14 we can use `t.Cleanup(func() { if err := <>; err != nil {..}}` to cover those errors, I will do this in pr number two of enabling errcheck.

ref #5059

crypto/internal/benchmarking/bench.go

@@ -37,7 +37,11 @@ func BenchmarkSigning(b *testing.B, priv crypto.PrivKey) {
 	message := []byte("Hello, world!")
 	b.ResetTimer()
 	for i := 0; i < b.N; i++ {
-		priv.Sign(message)
+		_, err := priv.Sign(message)
+
+		if err != nil {
+			b.FailNow()
+		}
 	}
 }
 

crypto/tmhash/hash_test.go

@@ -5,6 +5,7 @@ import (
 	"testing"
 
 	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
 
 	"github.com/tendermint/tendermint/crypto/tmhash"
 )
@@ -12,13 +13,15 @@ import (
 func TestHash(t *testing.T) {
 	testVector := []byte("abc")
 	hasher := tmhash.New()
-	hasher.Write(testVector)
+	_, err := hasher.Write(testVector)
+	require.NoError(t, err)
 	bz := hasher.Sum(nil)
 
 	bz2 := tmhash.Sum(testVector)
 
 	hasher = sha256.New()
-	hasher.Write(testVector)
+	_, err = hasher.Write(testVector)
+	require.NoError(t, err)
 	bz3 := hasher.Sum(nil)
 
 	assert.Equal(t, bz, bz2)
@@ -28,13 +31,15 @@ func TestHash(t *testing.T) {
 func TestHashTruncated(t *testing.T) {
 	testVector := []byte("abc")
 	hasher := tmhash.NewTruncated()
-	hasher.Write(testVector)
+	_, err := hasher.Write(testVector)
+	require.NoError(t, err)
 	bz := hasher.Sum(nil)
 
 	bz2 := tmhash.SumTruncated(testVector)
 
 	hasher = sha256.New()
-	hasher.Write(testVector)
+	_, err = hasher.Write(testVector)
+	require.NoError(t, err)
 	bz3 := hasher.Sum(nil)
 	bz3 = bz3[:tmhash.TruncatedSize]