drm/i915/fdinfo: Don't show engine classes not present

Stop displaying engine classes with no engines - it is not a huge problem
if they are shown, since the values will correctly be all zeroes, but it
does count as misleading.
Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Fixes: 055634e4 ("drm/i915: Expose client engine utilisation via fdinfo")
Cc: Umesh Nerlige Ramappa <umesh.nerlige.ramappa@intel.com>
Reviewed-by: Umesh Nerlige Ramappa <umesh.nerlige.ramappa@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220616140056.559074-1-tvrtko.ursulin@linux.intel.com

drivers/gpu/drm/i915/i915_drm_client.c

@@ -116,8 +116,9 @@ show_client_class(struct seq_file *m,
 		total += busy_add(ctx, class);
 	rcu_read_unlock();
 
-	seq_printf(m, "drm-engine-%s:\t%llu ns\n",
-		   uabi_class_names[class], total);
+	if (capacity)
+		seq_printf(m, "drm-engine-%s:\t%llu ns\n",
+			   uabi_class_names[class], total);
 
 	if (capacity > 1)
 		seq_printf(m, "drm-engine-capacity-%s:\t%u\n",