media: venus: Refactor hfi_buffer_alloc_mode_supported

Replace the old style single element array at the end of the struct with
a flex array.

The code does not allocate this structure, so the size change should not
be a problem.

This fixes the following cocci warning:
drivers/media/platform/qcom/venus/hfi_helper.h:1233:5-9: WARNING use flexible-array member instead (https://www.kernel.org/doc/html/latest/process/deprecated.html#zero-length-and-one-element-arrays

)

Signed-off-by: Ricardo Ribalda <ribalda@chromium.org>
Acked-by: Vikash Garodia <quic_vgarodia@quicinc.com>
Signed-off-by: Stanimir Varbanov <stanimir.k.varbanov@gmail.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>