usb: gsi: Prevent enabling data path if gsi is disconnected

If USB connect/disconnect happens too fast then there is a
possibility that for the connect case the state machine got
kicked in late lets say after disconnect. Now GSI driver will
go ahead and enable data path which can lead to SMMU fault.
Fix this by bailing out if gsi is in disconnected state.

Change-Id: I356ebd3fbac634f37e8eb6ff36a5a258f44a044b
Signed-off-by: Pratham Pratap <prathampratap@codeaurora.org>