tools: hv: fix a compile warning in snprintf

hv_kvp_daemon.c: In function .kvp_mac_to_if_name.:
hv_kvp_daemon.c:705:2: warning: format not a string literal and no format arguments [-Wformat-security]
  snprintf(dev_id, sizeof(dev_id), kvp_net_dir);
  ^
hv_kvp_daemon.c:705:2: warning: format not a string literal and no format arguments [-Wformat-security]

Signed-off-by: Weibing Zhang <atheism.zhang@gmail.com>
Signed-off-by: K. Y. Srinivasan <kys@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>