scsi-generic: avoid out-of-bounds access to VPD page list

scsi-generic: avoid out-of-bounds access to VPD page list

A device can report an excessive number of VPD pages when asked for a
list; this can cause an out-of-bounds access to buf in
scsi_generic_set_vpd_bl_emulation.  It should not happen, but
it is technically not incorrect so handle it: do not check any byte
past the allocation length that was sent to the INQUIRY command.

Reported-by: Max Reitz <mreitz@redhat.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>