mctp-bench: fix uninitialised warning for last_rc

We have a warning with optimisation enabled:

    ../src/mctp-bench.c:309:46: warning: ‘last_rc’ may be used uninitialized [-Wmaybe-uninitialized]
      309 |                 if (rc != (int)send_args.len && rc != last_rc) {

Signed-off-by: Jeremy Kerr <jk@codeconstruct.com.au>

Author: jk-ozlabs

src/mctp-bench.c

@@ -300,6 +300,10 @@ static int mctp_bench_send(struct mctp_bench_send_args send_args)
 
         hdr = (struct msg_header *)buf;
         hdr->magic = MAGIC_VAL;
+
+	/* will not match a sensible sendto() return value */
+	last_rc = 0;
+
         while (1) {
                 addr.smctp_tag = tag;
                 hdr->seq_no = sequence;