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

cmd/zpool/zpool_main.c

@@ -1065,7 +1065,7 @@ zpool_do_add(int argc, char **argv)
 				free(vname);
 			}
 		}
-		/* And finaly the spares */
+		/* And finally the spares */
 		if (nvlist_lookup_nvlist_array(poolnvroot, ZPOOL_CONFIG_SPARES,
 		    &sparechild, &sparechildren) == 0 && sparechildren > 0) {
 			hadspare = B_TRUE;

cmd/zpool/zpool_vdev.c

@@ -445,7 +445,7 @@ typedef struct replication_level {
 
 /*
  * N.B. For the purposes of comparing replication levels dRAID can be
- * considered functionally equivilant to raidz.
+ * considered functionally equivalent to raidz.
  */
 static boolean_t
 is_raidz_mirror(replication_level_t *a, replication_level_t *b,