Kernel crash via stale CXL decoder reference

Use-after-free in the Linux kernel CXL port driver allows local users to crash the kernel during out-of-order decoder teardown. An out-of-order switch-decoder reset aborts region cleanup but frees an endpoint decoder, so a later cxl_region_decode_reset() dereferences the stale object. Reachability requires a CXL region whose endpoints share a switch decoder and teardown outside allocation order; the bounded consequence is a kernel crash.