adb: libusb: recognize devices with multiple interfaces.

A bug was introduced by commit 8bf37d7a wherein we accidentally only
look at the first interface of a device when checking whether a USB
device was an ADB device or not.

Bug: http://b/38201318
Test: none
Change-Id: I8e8e0963c77cd2cb03538d926ab735f4b57e52b7