drivers/base/memory: fix memory block reference leak in poison accounting

In the Linux kernel, the following vulnerability has been resolved: drivers/base/memory: fix memory block reference leak in poison accounting memblk_nr_poison_inc() and memblk_nr_poison_sub() look up a memory block via find_memory_block_by_id(), which acquires a reference to the memory block device. Both helpers use the returned memory block without dropping that reference, leaking the device reference on each successful lookup. Drop the reference after updating nr_hwpoison.