staging: typec: tcpci: declare private structure as static

This fixes a sparse warning regarding an undeclared symbol. Since the
structure tcpci_tcpc_config is private to tcpci.c, it should be declared as
static.

Signed-off-by: Olivier Leveque <o_leveque@orange.fr>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>