scsi: pm80xx: Avoid -Wflex-array-member-not-at-end warnings

Comment out unused field 'residual_count' in a couple of structures, and
with this, fix the following -Wflex-array-member-not-at-end warnings:

drivers/scsi/pm8001/pm8001_hwi.h:342:33: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]
drivers/scsi/pm8001/pm80xx_hwi.h:561:32: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]

Reviewed-by: Jack Wang <[e-mail]>
Reviewed-by: John Garry <[e-mail]>
Signed-off-by: Gustavo A. R. Silva <[e-mail]>
Signed-off-by: Martin K. Petersen <[e-mail]>

drivers/scsi/pm8001/pm8001_hwi.h

···
 	__le32	status;
 	__le32	param;
 	__le32	ssptag_rescv_rescpad;
+
+	/* Must be last --ends in a flexible-array member. */
 	struct ssp_response_iu  ssp_resp_iu;
-	__le32	residual_count;
+	/* __le32  residual_count; */
 } __attribute__((packed, aligned(4)));
 
 

drivers/scsi/pm8001/pm80xx_hwi.h

···
 	__le32	status;
 	__le32	param;
 	__le32	ssptag_rescv_rescpad;
+
+	/* Must be last --ends in a flexible-array member. */
 	struct ssp_response_iu ssp_resp_iu;
-	__le32	residual_count;
+	/* __le32  residual_count; */
 } __attribute__((packed, aligned(4)));
 
 #define SSP_RESCV_BIT	0x00010000