esp.c: convert esp_reg_write() do_cmd path to check for SCSI phase instead

esp.c: convert esp_reg_write() do_cmd path to check for SCSI phase instead

Currently do_cmd is used to determine whether MESSAGE OUT and COMMAND phase data
is being accumulated in cmdfifo. Update esp_do_dma() to check directly for these
two SCSI phases instead.

Signed-off-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
Tested-by: Helge Deller <deller@gmx.de>
Tested-by: Thomas Huth <thuth@redhat.com>
Message-Id: <20240112125420.514425-45-mark.cave-ayland@ilande.co.uk>
Signed-off-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>