adb: win32: Unicode USB device names

Cleanup TODO and instead of (poorly) converting the device name from
wchar_t to char, just retrieve and store it as wchar_t, simplifying the
code.

This probably isn't necessary since device names are probably always
ASCII, but this cleans things up.

Change-Id: Ib780dcdc1e0e06b97b61e25d29a23874b35d7800
Signed-off-by: Spencer Low <CompareAndSwap@gmail.com>