entity_namecheck: doc comment: include space as allowed character

The helper function valid_char already allows it but
the doc comment was out of date.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Christian Schwarz <me@cschwarz.com>
Closes #9879

module/zcommon/zfs_namecheck.c

@@ -171,7 +171,7 @@ dataset_nestcheck(const char *path)
  * Where each component is made up of alphanumeric characters plus the following
  * characters:
  *
- *	[-_.:%]
+ *	[-_.: %]
  *
  * We allow '%' here as we use that character internally to create unique
  * names for temporary clones (for online recv).