staging: typec: tcpm: explicit_contract is always established

While in SNK_READY state, the explicit_contract seems to be
set to true irrespective of whether an explicit contract
was established for the current connection. TCPM also seems
to report the pwr_opmode as TYPEC_PWR_MODE_PD always once
the port gets into SNK_READY state. This isn't completely
true as port gets into the SNK_READY state for non-pd
type-c ports as well.

This patch sets the explicit_contract flag only when
the PS_READY message is received and the vbus has been
detected by the port controller.

Signed-off-by: Badhri Jagan Sridharan <Badhri@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>