drm/i915/gvt: remove the redundant info NULL check

The variable info is never NULL, which is checked by the caller. This
patch removes the redundant info NULL check logic.

Fixes: 695fbc08 ("drm/i915/gvt: replace the gvt_err with gvt_vgpu_err")
Signed-off-by: Tina Zhang <tina.zhang@intel.com>
Signed-off-by: Zhenyu Wang <zhenyuw@linux.intel.com>