adb: Have device usb_handle return io size

Previously, read and write would return 0
on success. Now it will return the number
of bytes read/write. This is more consistent
with other usb handles and is needed in order
to handle partial packets (for fastbootd).

Update usb_write in other usb handles
to return amount written.

Change transport_usb accordingly.

Test: adb works
Bug: 78793464
Change-Id: If07ff05fbc8120343f20661475d34f4e5ff805de