Fix typos in module/zfs/

Reviewed-by: Matt Ahrens <matt@delphix.com>
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 #9240

module/zfs/spa_errlog.c

@@ -31,7 +31,7 @@
  * and the current log.  All errors seen are logged to the current log.  When a
  * scrub completes, the current log becomes the last log, the last log is thrown
  * out, and the current log is reinitialized.  This way, if an error is somehow
- * corrected, a new scrub will show that that it no longer exists, and will be
+ * corrected, a new scrub will show that it no longer exists, and will be
  * deleted from the log when the scrub completes.
  *
  * The log is stored using a ZAP object whose key is a string form of the