UPSTREAM: USB: cdc-wdm: fix wdm_find_device* return value

UPSTREAM: USB: cdc-wdm: fix wdm_find_device* return value

A logic error made the wdm_find_device* functions
return a bogus pointer into static data instead of
the intended NULL no matching device was found.

Cc: stable <stable@vger.kernel.org> # v3.4+
Cc: Oliver Neukum <oliver@neukum.org>
Signed-off-by: Bjørn Mork <bjorn@mork.no>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
(cherry picked from commit 6a44886899ef8cc396e230e492e6a56a883889f3)

Change-Id: I80f21db165d6f1791c7dd6bf0f02e6deb25b77b7
Signed-off-by: Ben Chan <benchan@chromium.org>
Reviewed-on: https://gerrit.chromium.org/gerrit/35160
Reviewed-by: Olof Johansson <olofj@chromium.org>