drm/i915/sdvo: Check error return from intel_sdvo_get_value()

The current code assumes that 'enhancements' won't change in case of an
error, but this isn't guaranteed. Fix things by treating any error as a
lack of the given capability.

v2:
- Remove the now redundant init of enhancements. (Ville)

Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Imre Deak <imre.deak@intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1494408113-379-3-git-send-email-imre.deak@intel.com

drivers/gpu/drm/i915/intel_sdvo.c

@@ -2892,11 +2892,10 @@ static bool intel_sdvo_create_enhance_property(struct intel_sdvo *intel_sdvo,
 
 	BUILD_BUG_ON(sizeof(enhancements) != 2);
 
-	enhancements.response = 0;
-	intel_sdvo_get_value(intel_sdvo,
+	if (!intel_sdvo_get_value(intel_sdvo,
 				  SDVO_CMD_GET_SUPPORTED_ENHANCEMENTS,
-			     &enhancements, sizeof(enhancements));
-	if (enhancements.response == 0) {
+				  &enhancements, sizeof(enhancements)) ||
+	    enhancements.response == 0) {
 		DRM_DEBUG_KMS("No enhancement is supported\n");
 		return true;
 	}