radeon_hd: Fix crash of driver on multiple open

* open_count only got raised on initial open,
  subsequent opens didn't increment the counter
  thus when they exited the driver unloaded
  causing app_server to crash
* Thanks to hamishm for pointing out that
  the if checks the pre-increment number
* Resolves #10452
* Add a kdl debug command to radeon_hd

src/add-ons/kernel/drivers/graphics/radeon_hd/device.cpp

@@ -123,12 +123,15 @@ device_open(const char* name, uint32 /*flags*/, void** _cookie)
 
 	mutex_lock(&gLock);
 
-	if (info->open_count == 0) {
+	if (info->open_count++ == 0) {
 		// this device has been opened for the first time, so
 		// we allocate needed resources and initialize the structure
 		info->init_status = radeon_hd_init(*info);
 		if (info->init_status == B_OK) {
-			info->open_count++;
+#ifdef DEBUG_COMMANDS
+			add_debugger_command("radeonhd_reg", getset_register,
+				"dumps or sets the specified radeon_hd register");
+#endif
 		}
 	}