encoding/csv: indicate package of EOF in docs

The documentation listing err == EOF can be confusing to newcomers
to the language who are looking for the relevant documentation for
that error.

Change-Id: I301885950d0e1d0fbdf3a1892fca86eac7a0c616
Reviewed-on: https://go-review.googlesource.com/15806Reviewed-by: Andrew Gerrand <adg@golang.org>

src/encoding/csv/reader.go

@@ -155,7 +155,7 @@ func (r *Reader) Read() (record []string, err error) {
 
 // ReadAll reads all the remaining records from r.
 // Each record is a slice of fields.
-// A successful call returns err == nil, not err == EOF. Because ReadAll is
+// A successful call returns err == nil, not err == io.EOF. Because ReadAll is
 // defined to read until EOF, it does not treat end of file as an error to be
 // reported.
 func (r *Reader) ReadAll() (records [][]string, err error) {