vty/telnet_interface.c: avoid unneeded initialization

Unconditional initialization follows the structure definition,
so there is no need to do it twice. This prevents compiler
from warning about potential errors.

Change-Id: If9fd2826f132dfa203dda62940d93dbdfcfd92ac
diff --git a/src/vty/telnet_interface.c b/src/vty/telnet_interface.c
index c16b0b1..d44754c 100644
--- a/src/vty/telnet_interface.c
+++ b/src/vty/telnet_interface.c
@@ -210,7 +210,7 @@
 /*! callback from core VTY code about VTY related events */
 void vty_event(enum event event, int sock, struct vty *vty)
 {
-	struct vty_signal_data sig_data = { 0, };
+	struct vty_signal_data sig_data;
 	struct telnet_connection *connection = vty->priv;
 	struct osmo_fd *bfd;