upload/koji/uploadChunk: fix compilation errors

The API of kolo/xmlrpc changed after the commit that is shipped in
Fedora. Pin the vendored version to that and adjust the API usage.

This should make the RPM compile in both RHEL and Fedora.

Signed-off-by: Tom Gundersen <teg@jklm.no>

vendor/github.com/kolo/xmlrpc/decoder.go

@@ -130,9 +130,8 @@ func (dec *decoder) decodeValue(val reflect.Value) error {
 				ismap = true
 			} else if checkType(val, reflect.Interface) == nil && val.IsNil() {
 				var dummy map[string]interface{}
-				valType = reflect.TypeOf(dummy)
-				pmap = reflect.New(valType).Elem()
-				val.Set(pmap)
+				pmap = reflect.New(reflect.TypeOf(dummy)).Elem()
+				valType = pmap.Type()
 				ismap = true
 			} else {
 				return err