Fix typos in cmd/

Reviewed-by: Ryan Moeller <ryan@ixsystems.com>
Reviewed-by: Richard Laager <rlaager@wiktel.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Andrea Gelmini <andrea.gelmini@gelma.net>
Closes #9234

cmd/zdb/zdb.c

@@ -5391,7 +5391,7 @@ zdb_set_skip_mmp(char *target)
  * the name of the target pool.
  *
  * Note that the checkpointed state's pool name will be the name of
- * the original pool with the above suffix appened to it. In addition,
+ * the original pool with the above suffix appended to it. In addition,
  * if the target is not a pool name (e.g. a path to a dataset) then
  * the new_path parameter is populated with the updated path to
  * reflect the fact that we are looking into the checkpointed state.