drm/i915/gvt: do not check len & max_len for lri

lri ususally of variable len and far exceeding 127 dwords.

Fixes: 00a33be4 ("drm/i915/gvt: Add valid length check for MI variable commands")
Signed-off-by: Yan Zhao <yan.y.zhao@intel.com>
Acked-by: Zhenyu Wang <zhenyuw@linux.intel.com>
Signed-off-by: Zhenyu Wang <zhenyuw@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20200304095121.21609-1-yan.y.zhao@intel.com