go.crypto/openpgp/armor: update for NewBufferSize signature change

Fixes the go.crypto build.

R=r
CC=golang-dev
https://golang.org/cl/5641049

openpgp/armor/armor.go

@@ -155,7 +155,7 @@ func (r *openpgpReader) Read(p []byte) (n int, err error) {
 // given Reader is not usable after calling this function: an arbitrary amount
 // of data may have been read past the end of the block.
 func Decode(in io.Reader) (p *Block, err error) {
-	r, _ := bufio.NewReaderSize(in, 100)
+	r := bufio.NewReaderSize(in, 100)
 	var line []byte
 	ignoreNext := false