target: Re-add explict zeroing of INQUIRY bounce buffer memory

This patch fixes a regression in spc_emulate_inquiry() code where the
local scope bounce buffer was no longer getting it's memory zeroed,
causing various problems with SCSI initiators that depend upon areas
of INQUIRY EVPD=0x83 payload having been zeroed.

This bug was introduced with the following v3.7-rc1 patch + CC'ed
stable commit:

commit ffe7b0e9
Author: Paolo Bonzini <pbonzini@redhat.com>
Date:   Fri Sep 7 17:30:38 2012 +0200

    target: support zero allocation length in INQUIRY

Go ahead and re-add the missing memset of bounce buffer memory to be
copied into the outgoing se_cmd descriptor kmapped SGL payload.

Reported-by: Kelsey Prantis <kelsey.prantis@intel.com>
Cc: Kelsey Prantis <kelsey.prantis@intel.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Andy Grover <agrover@redhat.com>
Cc: stable@vger.kernel.org
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>