USB: usbfs: fix potential infoleak in devio

The stack object “ci” has a total size of 8 bytes. Its last 3 bytes
are padding bytes which are not initialized and leaked to userland
via “copy_to_user”.

Bug: 28619695
Change-Id: I170754d659d0891c075f85211b5e3970b114f097
Signed-off-by: Kangjie Lu <kjlu@gatech.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>