drivers/block/DAC960: fix DAC960_V2_IOCTL_Opcode_T -Wenum-compare warning

Fixed compiler warning:

comparison between ‘DAC960_V2_IOCTL_Opcode_T’ and ‘enum <anonymous>’

Renamed enum, added a new enum for SCSI_10.CommandOpcode in
DAC960_V2_ProcessCompletedCommand().

Signed-off-by: Danny Kukawka <danny.kukawka@bisect.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>