TBR: fix(flags): bug fix for the '-prefix' flag

Change-Id: I443b1bea68482ff2b1e08e19a47331f4aa362359
diff --git a/madb.go b/madb.go
index a335899..ca35d91 100644
--- a/madb.go
+++ b/madb.go
@@ -370,8 +370,8 @@
 // Invokes the sub command on all the devices in parallel.
 func (r subCommandRunner) Run(env *cmdline.Env, args []string) error {
 	prefixFlag = strings.ToLower(prefixFlag)
-	if prefixFlag != "auto" && prefixFlag != "serial" && prefixFlag != "none" {
-		return fmt.Errorf(`The -prefix flag value must be one of "auto", "serial", or "none".`)
+	if prefixFlag != "name" && prefixFlag != "serial" && prefixFlag != "none" {
+		return fmt.Errorf(`The -prefix flag value must be one of "name", "serial", or "none".`)
 	}
 
 	if err := startAdbServer(); err != nil {