usb: musb/ux500: Use dma_request_chan() instead dma_request_slave_channel()

dma_request_slave_channel() is a wrapper on top of dma_request_chan()
eating up the error code.

Signed-off-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
Signed-off-by: Bin Liu <b-liu@ti.com>
Link: https://lore.kernel.org/r/20200115132547.364-19-b-liu@ti.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>