drm/i915/gvt: Fix relocation of shadow bb

set_gma_to_bb_cmd() is completely bogus - it is (incorrectly) applying
the rules to read a GTT offset from a command as opposed to writing the
GTT offset. And to cap it all set_gma_to_bb_cmd() is called within a list
iterator of the most strange construction.

Fixes: be1da707 ("drm/i915/gvt: vGPU command scanner")
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Zhenyu Wang <zhenyuw@linux.intel.com>
Cc: Zhi Wang <zhi.a.wang@intel.com>
Cc: Yulei Zhang <yulei.zhang@intel.com>
Cc: <drm-intel-fixes@lists.freedesktop.org> # v4.10-rc1+
Tested-by: Tina Zhang <tina.zhang@intel.com>
Signed-off-by: Zhenyu Wang <zhenyuw@linux.intel.com>