rndis_host: fix oops when query for OID_GEN_PHYSICAL_MEDIUM fails

When query for OID_GEN_PHYSICAL_MEDIUM fails, uninitialized pointer
'phym' is being accessed in generic_rndis_bind(), resulting OOPS.
Patch fixes phym to be initialized and setup correctly when
rndis_query() for physical medium fails.

Bug was introduced by following commit:
commit 039ee17d1baabaa21783a0d5ab3e8c6d8c794bdf
Author: Jussi Kivilinna <jussi.kivilinna@mbnet.fi>
Date:   Sun Jan 27 23:34:33 2008 +0200

Reported-by: Dmitri Monakhov <dmonakhov@openvz.org>
Signed-off-by: Jussi Kivilinna <jussi.kivilinna@mbnet.fi>
Acked-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Jeff Garzik <jeff@garzik.org>