zram: fix out-of-bounds access in read_block_state()

In the Linux kernel, the following vulnerability has been resolved: zram: fix out-of-bounds access in read_block_state() read_block_state() calculates nr_pages before taking dev_lock. If the device is reset and reinitialized with a smaller disksize before lock acquisition, nr_pages still describes the old table. The subsequent loop can then call slot_lock() past the end of the newly allocated table. Read disksize after acquiring dev_lock and checking that the device is initialized. The read lock then keeps the table and its bound stable for the duration of the scan.