drm/i915/gvt: Remove duplicated register accessible check

Looks this duplication was missed in code rebase. Remove extra check.

Cc: Yan Zhao <yan.y.zhao@intel.com>
Fixes: 02dd2b12

 ("drm/i915/gvt: unify lri cmd handler and mmio handlers")
Reviewed-by: Colin Xu <colin.xu@intel.com>
Signed-off-by: Zhenyu Wang <zhenyuw@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20210414084813.3763353-2-zhenyuw@linux.intel.com