drm/i915/perf: remove user triggerable warn

Don't throw a warning if we are given an invalid property id. While
here let's also bring back Robert' original idea of catching unhandled
enumeration values at compile time.

Fixes: eec688e1420d ("drm/i915: Add i915 perf infrastructure")
Signed-off-by: Matthew Auld <matthew.auld@intel.com>
Cc: Robert Bragg <robert@sixbynine.org>
Reviewed-by: Robert Bragg <robert@sixbynine.org>
Signed-off-by: Mika Kuoppala <mika.kuoppala@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20170327203236.18276-1-matthew.auld@intel.com

drivers/gpu/drm/i915/i915_perf.c

@@ -1794,6 +1794,11 @@ static int read_properties_unlocked(struct drm_i915_private *dev_priv,
 		if (ret)
 			return ret;
 
+		if (id == 0 || id >= DRM_I915_PERF_PROP_MAX) {
+			DRM_DEBUG("Unknown i915 perf property ID\n");
+			return -EINVAL;
+		}
+
 		switch ((enum drm_i915_perf_property_id)id) {
 		case DRM_I915_PERF_PROP_CTX_HANDLE:
 			props->single_context = 1;
@@ -1863,9 +1868,8 @@ static int read_properties_unlocked(struct drm_i915_private *dev_priv,
 			props->oa_periodic = true;
 			props->oa_period_exponent = value;
 			break;
-		default:
+		case DRM_I915_PERF_PROP_MAX:
 			MISSING_CASE(id);
-			DRM_DEBUG("Unknown i915 perf property ID\n");
 			return -EINVAL;
 		}