gpio: fix failing tests

gpiodriver_test.go

@@ -1,6 +1,9 @@
 package embd
 
-import "testing"
+import (
+	"testing"
+	"time"
+)
 
 type fakeDigitalPin struct {
 	n int
@@ -22,6 +25,10 @@ func (*fakeDigitalPin) Write(val int) error {
 	return nil
 }
 
+func (*fakeDigitalPin) TimePulse(state int) (time.Duration, error) {
+	return 0, nil
+}
+
 func (*fakeDigitalPin) ActiveLow(b bool) error {
 	return nil
 }