scsi: mvumi: Replace 1-element arrays with flexible array members

scsi: mvumi: Replace 1-element arrays with flexible array members

One-element arrays (and multi-element arrays being treated as dynamically
sized) are deprecated[1] and are being replaced with flexible array members
in support of the ongoing efforts to tighten the FORTIFY_SOURCE routines on
memcpy(), correctly instrument array indexing with UBSAN_BOUNDS, and to
globally enable -fstrict-flex-arrays=3.

Replace one-element arrays with flexible-array member in struct
mvumi_msg_frame, struct mvumi_rsp_frame, and struct mvumi_hs_header,
adjusting the explicit sizing calculations at the same time.

This results in no functional differences in binary output. An explicit add
is now folded into the size calculation:

│       mov    0x1070(%r14),%eax
│ -     add    $0x4,%eax
│ -     movabs $0xfffffffdc,%rbx
│ +     movabs $0xfffffffe0,%rbx
│       add    %rax,%rbx

[1] https://www.kernel.org/doc/html/latest/process/deprecated.html#zero-length-and-one-element-arrays

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: linux-scsi@vger.kernel.org
Signed-off-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Link: https://lore.kernel.org/r/20230105011143.never.569-kees@kernel.org
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>