Add explicit close of Scanner input

The UsbDeviceManager is using a Scanner to identify
the ALSA card/device numbers to use for USB Gadget
audio, with a FileInputStream as its input.

Since FileInputStream implements the Closeable interface
it provides a close() method that should be explictly
called in order to close the stream source and release
any system resources that it might hold.

Change-Id: Ia0ff86d1f3cdf8916becec9c8603915dcbf4d2c8
UsbDebuggingManager: Fix multiple NPEs toggling USB debugging

Change-Id: I7ac039fe51a32d35ef00eaa71accb85cd57d4d8a
Signed-off-by: atl4ntis <atl4ntis@gmail.com>