binder: fix incorrect cmd to binder_stat_br

commit 26549d17 ("binder: guarantee txn complete / errors delivered
in-order") passed the locally declared and undefined cmd
to binder_stat_br() which results in a bogus cmd field in a trace
event and BR stats are incremented incorrectly.

Change to use e->cmd which has been initialized.

Signed-off-by: Todd Kjos <tkjos@google.com>
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Fixes: 26549d17 ("binder: guarantee txn complete / errors delivered in-order")
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>