scsi: set dma direction to NONE for TEST UNIT READY

SCSI device scan code was executing TEST UNIT READY command without
explicitly setting dma direction in struct scsi_cmd to NONE, so command
was passed to driver with dma direction set to DMA_FROM_DEVICE,
inherited from older usage.

With WDC SDINDDH6-64G ufs device, that caused TEST UNIT READY to
return error.

Fix that, by explicitly setting dma direction to NONE for
TEST UNIT READY, and restoring it back DMA_FROM_DEVICE for the
following READ CAPACITY.

Signed-off-by: Nikita Yushchenko <nikita.yoush@cogentembedded.com>
Reviewed-by: Marek Vasut <marex@denx.de>