ASoC: aw88395: use struct_size() and __counted_by() for aw_container

ASoC: aw88395: use struct_size() and __counted_by() for aw_container

The firmware container allocations passed cont->size + sizeof(int) to
kzalloc(), which was wrong: the struct contains an int len followed by a
u8 data[] flexible array. It ended up being the same as the struct's
size is only the int member but still wrong.

Use the modern struct_size helper for this.

Add __counted_by for extra runtime analysis.

Assisted-by: Claude:Opus-4.7
Signed-off-by: Rosen Penev <rosenp@gmail.com>
Link: https://patch.msgid.link/20260523011749.101555-1-rosenp@gmail.com
Signed-off-by: Mark Brown <broonie@kernel.org>