USB: CDC: fix sanity checks in CDC union parser

USB: CDC: fix sanity checks in CDC union parser

A few checks checked for the size of the pointer to a structure
instead of the structure itself. Copy & paste issue presumably.

Fixes: e4c6fb7794982 ("usbnet: move the CDC parser into USB core")
Cc: stable <stable@vger.kernel.org>
Reported-by: syzbot+45a53506b65321c1fe91@syzkaller.appspotmail.com
Signed-off-by: Oliver Neukum <oneukum@suse.com>
Link: https://lore.kernel.org/r/20190813093541.18889-1-oneukum@suse.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>