coresight tmc etr: Make memory check consistent in the same function

While operating from sysFS the TMC-ETR driver needs to make sure it has
memory to work with but doesn't allocate memory uselessly either.  Since
the main memory handle for this driver is drvdata::vaddr, use it throughout
function tmc_enable_etr_sink_sysfs() so that things are consistent.

Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/hwtracing/coresight/coresight-tmc-etr.c

@@ -153,11 +153,11 @@ static int tmc_enable_etr_sink_sysfs(struct coresight_device *csdev)
 		goto out;
 
 	/*
-	 * If drvdata::buf == NULL, use the memory allocated above.
+	 * If drvdata::vaddr == NULL, use the memory allocated above.
 	 * Otherwise a buffer still exists from a previous session, so
 	 * simply use that.
 	 */
-	if (drvdata->buf == NULL) {
+	if (drvdata->vaddr == NULL) {
 		used = true;
 		drvdata->vaddr = vaddr;
 		drvdata->paddr = paddr;