Replace clk_lookup.con_id with clk_lookup.dev_id entries for twi clk

The old driver used con_id clock entries. Convert to use dev_id
for clock lookup via standard method.

Signed-off-by: Nikolaus Voss <n.voss@weinmann.de>
Tested-by: Ludovic Desroches <ludovic.desroches@atmel.com>
Reviewed-by: Nicolas Ferre <nicolas.ferre@atmel.com>
Signed-off-by: Wolfram Sang <w.sang@pengutronix.de>