drm/i915/huc: Avoid attempting to authenticate non-existent fw

HuC authentication is called even if HuC firmware is not present in the
system, leading to NULL ptr dereference on not allocated gem_object.
Let's avoid trying to authenticate HuC if its firmware is not loaded
successfully.

Fixes: dac84a3 ("drm/i915/huc: Support HuC authentication")

v2: Check inside the auth function, split the assert (Michał)
v3: Oops, hit send before compiling, s/huc_fw/huc->fw

Cc: Anusha Srivatsa <anusha.srivatsa@intel.com>
Cc: Arkadiusz Hiler <arkadiusz.hiler@intel.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Michal Wajdeczko <michal.wajdeczko@intel.com>
Signed-off-by: Michał Winiarski <michal.winiarski@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20170120192348.2049-1-michal.winiarski@intel.com
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>

drivers/gpu/drm/i915/intel_huc.c

@@ -299,6 +299,9 @@ void intel_guc_auth_huc(struct drm_i915_private *dev_priv)
 	int ret;
 	u32 data[2];
 
+	if (huc->fw.load_status != INTEL_UC_FIRMWARE_SUCCESS)
+		return;
+
 	vma = i915_gem_object_ggtt_pin(huc->fw.obj, NULL, 0, 0,
 				PIN_OFFSET_BIAS | GUC_WOPCM_TOP);
 	if (IS_ERR(vma)) {