i2c: at91: Use dma_request_chan() directly for channel request

dma_request_slave_channel_reason() is:
#define dma_request_slave_channel_reason(dev, name) \
	dma_request_chan(dev, name)

Signed-off-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
Acked-by: Ludovic Desroches <ludovic.desroches@microchip.com>
Reviewed-by: Vinod Koul <vkoul@kernel.org>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>