tunables: fix spelling

Three occurences with an 'e', and all of them mine. Maybe it's an
British thing?

Sponsored-by: https://despairlabs.com/sponsor/
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Alexander Motin <mav@FreeBSD.org>
Reviewed-by: Pavel Snajdr <snajpa@snajpa.net>
Signed-off-by: Rob Norris <robn@despairlabs.com>
Closes #17377

module/zfs/ddt.c

@@ -153,7 +153,7 @@
  * storage object (ie ZAP) as normal. OpenZFS will try hard to flush enough to
  * keep up with the rate of change on dedup entries, but not so much that it
  * would impact overall throughput, and not using too much memory. See the
- * zfs_dedup_log_* tuneables in zfs(4) for more details.
+ * zfs_dedup_log_* tunables in zfs(4) for more details.
  *
  * ## Repair IO
  *

module/zfs/dmu.c

@@ -2373,7 +2373,7 @@ dmu_write_policy(objset_t *os, dnode_t *dn, int level, int wp, zio_prop_t *zp)
 
 		if (dmu_ddt_copies > 0) {
 			/*
-			 * If this tuneable is set, and this is a write for a
+			 * If this tunable is set, and this is a write for a
 			 * dedup entry store (zap or log), then we treat it
 			 * something like ZFS_REDUNDANT_METADATA_MOST on a
 			 * regular dataset: this many copies, and one more for