error: Use error_reportf_err() where appropriate

Replace

    error_report("...: %s", ..., error_get_pretty(err));

by

    error_reportf_err(err, "...: ", ...);

One of the replaced messages lacked a colon.  Add it.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-Id: <20200505101908.6207-6-armbru@redhat.com>
diff --git a/chardev/char-socket.c b/chardev/char-socket.c
index e77699d..db253d4 100644
--- a/chardev/char-socket.c
+++ b/chardev/char-socket.c
@@ -138,8 +138,9 @@
     SocketChardev *s = SOCKET_CHARDEV(chr);
 
     if (!s->connect_err_reported) {
-        error_report("Unable to connect character device %s: %s",
-                     chr->label, error_get_pretty(err));
+        error_reportf_err(err,
+                          "Unable to connect character device %s: ",
+                          chr->label);
         s->connect_err_reported = true;
     }
     qemu_chr_socket_restart_timer(chr);