Claude review: dma-buf: heaps: use max3() in dma_heap_ioctl

[Claude Code Review Bot <claude-review@example.com>]

Patch Review

**Status:** Looks good.

The change replaces:
```c
ksize = max(max(in_size, out_size), drv_size);
```
with:
```c
ksize = max3(in_size, out_size, drv_size);
```

This is a straightforward substitution. `max3()` is defined in `include/linux/minmax.h:152` and is available in this compilation unit through the existing include chain. The three arguments (`in_size`, `out_size`, `drv_size`) are all the same type (`unsigned int` derived from the ioctl size encoding), so there are no type-promotion surprises.

The commit message is accurate and concise. The Signed-off-by is present.

**Reviewed-by worthy:** Yes, no issues found.

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