CVE-2026-72224: nvdimm/btt: Free arenas on btt_init() error paths

In the Linux kernel, the following vulnerability has been resolved:

nvdimm/btt: Free arenas on bttinit() error paths

The arenas allocated by discoverarenas() or createarenas() are not freed on some error paths in bttinit(). This leaks memory when BTT initialization fails.

Call freearenas() from the affected error paths to release the allocations.

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