USB: usbfs: don't leak kernel data in siginfo

When a signal is delivered, the information in the siginfo structure
is copied to userspace.  Good security practice dicatates that the
unused fields in this structure should be initialized to 0 so that
random kernel stack data isn't exposed to the user.  This patch adds
such an initialization to the two places where usbfs raises signals.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Reported-by: Dave Mielke <dave@mielke.cc>
CC: <stable@vger.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>