USB: rndis_host: debug info clobbered before it is logged

The MTU throttle-down if a RNDIS device doesn't support a particular
packet size is being incorrectly logged.  The attempted packet size is
being clobbered before it gets logged.

First patch; please inform if I'm doing this incorrectly.  Diff'd
against latest official source as per the FAQ; forward port to current
git version is straightforward.

Signed-off-by: George Nassar <george.nassar@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>