scsi: hptiop: Replace one-element array with flexible-array member

One-element arrays are deprecated, and we are replacing them with flexible
array members instead. So, replace one-element array with flexible-array
member in struct hpt_iop_request_scsi_command and refactor the rest of the
code, accordingly.

The following pieces of code suggest that the one element of array sg_list
in struct hpt_iop_request_scsi_command is not taken into account when
calculating the total size for both struct hpt_iop_request_scsi_command and
the maximum number of elements sg_list will contain:

1047         req->header.size = cpu_to_le32(
1048                                 sizeof(struct hpt_iop_request_scsi_command)
1049                                  - sizeof(struct hpt_iopsg)
1050                                  + sg_count * sizeof(struct hpt_iopsg));

1400         req_size = sizeof(struct hpt_iop_request_scsi_command)                            1401                 + sizeof(struct hpt_iopsg) * (hba->max_sg_descriptors - 1);

So it's safe to replace the one-element array with a flexible-array member
and update the code above, accordingly: now we don't need to subtract
sizeof(struct hpt_iopsg) from sizeof(struct hpt_iop_request_scsi_command)
because this is implicitly done by the flex-array transformation.

Link: https://github.com/KSPP/linux/issues/79
Link: https://github.com/KSPP/linux/issues/205
Link: https://lore.kernel.org/r/6238ccf37798e36d783f5ce5e483e6837e98be79.1663865333.git.gustavoars@kernel.org


Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>