media: venus: hfi_msgs.h: Replace one-element arrays with flexible-array members

There is a regular need in the kernel to provide a way to declare having
a dynamically sized set of trailing elements in a structure. Kernel code
should always use “flexible array members”[1] for these cases. The older
style of one-element or zero-length arrays should no longer be used[2].

Use flexible-array members in struct hfi_msg_sys_property_info_pkt and
hfi_msg_session_property_info_pkt instead of one-element arrays, and
refactor the code accordingly.

Also, this helps with the ongoing efforts to enable -Warray-bounds by
fixing the following warnings:

  CC [M]  drivers/media/platform/qcom/venus/hfi_msgs.o
drivers/media/platform/qcom/venus/hfi_msgs.c: In function ‘hfi_sys_property_info’:
drivers/media/platform/qcom/venus/hfi_msgs.c:246:35: warning: array subscript 1 is above array bounds of ‘u32[1]’ {aka ‘unsigned int[1]’} [-Warray-bounds]
  246 |  if (req_bytes < 128 || !pkt->data[1] || pkt->num_properties > 1)
      |                          ~~~~~~~~~^~~
drivers/media/platform/qcom/venus/hfi_msgs.c: In function ‘hfi_session_prop_info’:
drivers/media/platform/qcom/venus/hfi_msgs.c:342:62: warning: array subscript 1 is above array bounds of ‘u32[1]’ {aka ‘unsigned int[1]’} [-Warray-bounds]
  342 |  if (!req_bytes || req_bytes % sizeof(*buf_req) || !pkt->data[1])
      |                                                     ~~~~~~~~~^~~

[1] https://en.wikipedia.org/wiki/Flexible_array_member
[2] https://www.kernel.org/doc/html/v5.9/process/deprecated.html#zero-length-and-one-element-arrays

Link: https://github.com/KSPP/linux/issues/79
Link: https://github.com/KSPP/linux/issues/109

Co-developed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Signed-off-by: Stanimir Varbanov <stanimir.varbanov@linaro.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>