logd: fix LogStatistics::format freeing wrong pointer

Fixes a leak and use-after-free if a client passes in an
already-allocated target buffer (currently none do)

Change-Id: Ie20c30bd5ba31e1b6db73885bd9d2ebd7e40dc27
Signed-off-by: Greg Hackmann <ghackmann@google.com>

logd/LogStatistics.cpp

@@ -401,7 +401,7 @@ void LogStatistics::format(char **buf,
     const unsigned short spaces_total = 19;
 
     if (*buf) {
-        free(buf);
+        free(*buf);
         *buf = NULL;
     }