transport: fix segfault in setup_command_handler()

Commit 93f2afa45f dropped the sentinel off the end
of the command_registrants[] array.  The loop immediately
following the initialization will walk right off the end.

Signed-off-by: Stacey Sheldon <stac@solidgoldbomb.org>

src/openocd.c

@@ -235,6 +235,7 @@ struct command_context *setup_command_handler(Jim_Interp *interp)
 		&nand_register_commands,
 		&pld_register_commands,
 		&mflash_register_commands,
+		NULL
 	};
 	for (unsigned i = 0; NULL != command_registrants[i]; i++)
 	{