usb: core: fix information leak to userland

Structure usbdevfs_connectinfo is copied to userland with padding byted
after "slow" field uninitialized.  It leads to leaking of contents of
kernel stack memory.

Signed-off-by: Vasiliy Kulikov <segooon@gmail.com>
Cc: stable <stable@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>