Fix zdb_read_block using zio after it is destroyed
The checksum display code of zdb_read_block uses a zio
to read in the block and then calls zio_checksum_compute.
Use a new zio in the call to zio_checksum_compute not the zio
from the read which has been destroyed by zio_wait.
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov> Reviewed-by: Igor Kozhukhov <igor@dilos.org> Signed-off-by: Paul Zuchowski <pzuchowski@datto.com>
Closes #9644
Closes #9657