esp: determine transfer direction directly from SCSI phase

esp: determine transfer direction directly from SCSI phase

The transfer direction is currently determined by checking the sign of ti_size
but as this series progresses ti_size can be zero at the end of the transfer.

Use the SCSI phase to determine the transfer direction as used in other SCSI
controller implementations.

Signed-off-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: Laurent Vivier <laurent@vivier.eu>
Message-Id: <20210304221103.6369-9-mark.cave-ayland@ilande.co.uk>