drivers/i2c/busses: use correct type for dma_map/unmap

dma_{un}map_* uses 'enum dma_data_direction' not 'enum dma_transfer_direction'.

Signed-off-by: Wolfram Sang <wsa@the-dreams.de>
Acked-by: Ludovic Desroches <ludovic.desroches@atmel.com>
Cc: stable@kernel.org