drm/i915: Avoid overflowing the DP link rate arrays

Complain loudly if we ever attempt to overflow the the supported_rates[]
array. This should never happen since the sink_rates[] array will always
be smaller or of equal size. But should someone change that we want to
catch it without scribblign over the stack.
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Sonika Jindal <sonika.jindal@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/intel_dp.c

@@ -1203,6 +1203,8 @@ static int intersect_rates(const int *source_rates, int source_len,
 
 	while (i < source_len && j < sink_len) {
 		if (source_rates[i] == sink_rates[j]) {
+			if (WARN_ON(k >= DP_MAX_SUPPORTED_RATES))
+				return k;
 			supported_rates[k] = source_rates[i];
 			++k;
 			++i;