build: Fix build when WITH_HAL is defined

Commit 7c9a2d88 missed inclusion of virstring.h in a few places
when WITH_HAL is defined, causing build failures.

src/node_device/node_device_driver.c

@@ -33,6 +33,7 @@
 #include "datatypes.h"
 #include "viralloc.h"
 #include "virlog.h"
+#include "virstring.h"
 #include "node_device_conf.h"
 #include "node_device_hal.h"
 #include "node_device_driver.h"

src/node_device/node_device_hal.c

@@ -39,6 +39,7 @@
 #include "virlog.h"
 #include "node_device_driver.h"
 #include "virdbus.h"
+#include "virstring.h"
 
 #define VIR_FROM_THIS VIR_FROM_NODEDEV