Stop Detected interrupt is triggered when a Stop bit is detected on
the bus, which indicates the end of the current transfer.

When the end of a transfer is indicated by the Stop Detected interrupt,
drain the FIFO and signal completion for the transaction.
Signed-off-by: Sifan Naeem <sifan.naeem@imgtec.com>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>