scsi: megaraid_sas: Convert union megasas_sgl to flex-arrays

scsi: megaraid_sas: Convert union megasas_sgl to flex-arrays

In the ongoing effort to replace all fake flexible arrays with true
flexible arrays, replace the sge32, sge64, and sge_skinny members of union
megasas_sgl with true flexible arrays. No binary differences are seen after
this change; sizes were already being manually calculated using the member
struct sizes directly.

Cc: Kashyap Desai <kashyap.desai@broadcom.com>
Cc: Sumit Saxena <sumit.saxena@broadcom.com>
Cc: Shivasharan S <shivasharan.srikanteshwara@broadcom.com>
Cc: "James E.J. Bottomley" <jejb@linux.ibm.com>
Cc: "Martin K. Petersen" <martin.petersen@oracle.com>
Cc: Gustavo A. R. Silva <gustavoars@kernel.org>
Cc: megaraidlinux.pdl@broadcom.com
Cc: linux-scsi@vger.kernel.org
Signed-off-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20230511220957.never.919-kees@kernel.org
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>