Improve the error handling in i2c_imx_dma_request() and let it return an error
indication that the caller then can handle accordingly.

Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de>
Acked-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>