spi/spi-atmel: status information passed through controller data

The status of transfer is stored in controller data structure
so that it can be used not only by atmel_spi_msg_done() function.
This will be useful for upcoming dmaengine enabled driver.

Signed-off-by: Nicolas Ferre <nicolas.ferre@atmel.com>
Signed-off-by: Wenyou Yang <wenyou.yang@atmel.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>