Make zdb -R scale less poorly

zdb -R with :d tries to use gzip decompression 9 times per size.
There's absolutely no reason for that, they're all the same
decompressor.

Reviewed-by: Brian Atkinson <batkinson@lanl.gov>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Rich Ercolani <rincebrain@gmail.com>
Closes #15726