Fix various typos

Correct an assortment of typos throughout the code base.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Matthew Ahrens <mahrens@delphix.com>
Reviewed-by: Ryan Moeller <ryan@iXsystems.com>
Signed-off-by: Andrea Gelmini <andrea.gelmini@gelma.net>
Closes #11774

module/zfs/vdev_raidz.c

@@ -1984,7 +1984,7 @@ raidz_reconstruct(zio_t *zio, int *ltgts, int ntgts, int nparity)
  *      2   4 5  first: increment to 3
  *        3 4 5  done
  *
- * This strategy works for dRAID but is less effecient when there are a large
+ * This strategy works for dRAID but is less efficient when there are a large
  * number of child vdevs and therefore permutations to check. Furthermore,
  * since the raidz_map_t rows likely do not overlap reconstruction would be
  * possible as long as there are no more than nparity data errors per row.