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/os/freebsd/zfs/abd_os.c

@@ -306,7 +306,7 @@ void
 abd_free_linear_page(abd_t *abd)
 {
 	/*
-	 * FreeBSD does not have have scatter linear pages
+	 * FreeBSD does not have scatter linear pages
 	 * so there is an error.
 	 */
 	VERIFY(0);

module/os/freebsd/zfs/zfs_vnops_os.c

@@ -3577,7 +3577,7 @@ zfs_symlink(znode_t *dzp, const char *name, vattr_t *vap,
 
 	/*
 	 * Create a new object for the symlink.
-	 * for version 4 ZPL datsets the symlink will be an SA attribute
+	 * for version 4 ZPL datasets the symlink will be an SA attribute
 	 */
 	zfs_mknode(dzp, vap, tx, cr, 0, &zp, &acl_ids);
 

module/os/freebsd/zfs/zio_crypt.c

@@ -114,7 +114,7 @@
  * Similarly to ZIL blocks, the core part of each dnode_phys_t needs to be left
  * in plaintext for scrubbing and claiming, but the bonus buffers might contain
  * sensitive user data. The function zio_crypt_init_uios_dnode() handles parsing
- * which which pieces of the block need to be encrypted. For more details about
+ * which pieces of the block need to be encrypted. For more details about
  * dnode authentication and encryption, see zio_crypt_init_uios_dnode().
  *
  * OBJECT SET AUTHENTICATION:

module/os/freebsd/zfs/zvol_os.c

@@ -761,7 +761,7 @@ zvol_cdev_read(struct cdev *dev, struct uio *uio_s, int ioflag)
 	volsize = zv->zv_volsize;
 	/*
 	 * uio_loffset == volsize isn't an error as
-	 * its required for EOF processing.
+	 * it's required for EOF processing.
 	 */
 	if (zfs_uio_resid(&uio) > 0 &&
 	    (zfs_uio_offset(&uio) < 0 || zfs_uio_offset(&uio) > volsize))