usb: pd: Decrease FIRST_SOURCE_CAP_TIME to 100ms

Now that there is the potential for cable discovery being
performed before starting to send Source_Capabilities, the
additional delay may push it beyond the spec max of
tFirstSourceCap (250ms). Decrease the FIRST_SOURCE_CAP_TIME
delay to 100ms to give some more room.

Change-Id: I2b92b31ebf966f549b2182aea594e02993217e9a
Signed-off-by: Jack Pham <jackp@codeaurora.org>