staging: typec: tcpci: Only touch target bit when enable vconn

We need regmap_update_bits to avoid touch any other bits when
enable or disable vconn.

Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Reviewed-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Signed-off-by: Li Jun <jun.li@nxp.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>