coresight: checking for NULL string in coresight_name_match()

Connection child names associated to ports can sometimes be NULL,
which is the case when booting a system on QEMU or when the Coresight
power domain isn't switched on.

This patch is adding a check to make sure a NULL string isn't fed
to strcmp(), something that avoid crashing the system.

Cc: <stable@vger.kernel.org> # v3.18+
Reported-by: Tyler Baker <tyler.baker@linaro.org>
Signed-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/hwtracing/coresight/coresight.c

@@ -548,7 +548,7 @@ static int coresight_name_match(struct device *dev, void *data)
 	to_match = data;
 	i_csdev = to_coresight_device(dev);
 
-	if (!strcmp(to_match, dev_name(&i_csdev->dev)))
+	if (to_match && !strcmp(to_match, dev_name(&i_csdev->dev)))
 		return 1;
 
 	return 0;