[SCSI] Return NEEDS_RETRY for eh commands with status BUSY

When the transport is busy and we're sending an EH command drivers
occasionally return 'BUSY'. As this in most cases is the TUR
command sent as part of the error recovery this is a sure way
to make the error recovery escalate. Returning 'NEEDS_RETRY'
here will just retry the TUR command and eventually abort the
original command, thus making error handling far smoother.

Signed-off-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: James Bottomley <James.Bottomley@suse.de>