Fix typos in module/zfs/

Reviewed-by: Matt Ahrens <matt@delphix.com>
Reviewed-by: Ryan Moeller <ryan@ixsystems.com>
Reviewed-by: Richard Laager <rlaager@wiktel.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Andrea Gelmini <andrea.gelmini@gelma.net>
Closes #9240

module/zfs/dbuf.c

@@ -2275,7 +2275,7 @@ dmu_buf_will_dirty_impl(dmu_buf_t *db_fake, int flags, dmu_tx_t *tx)
 	ASSERT(!zfs_refcount_is_zero(&db->db_holds));
 
 	/*
-	 * Quick check for dirtyness.  For already dirty blocks, this
+	 * Quick check for dirtiness.  For already dirty blocks, this
 	 * reduces runtime of this function by >90%, and overall performance
 	 * by 50% for some workloads (e.g. file deletion with indirect blocks
 	 * cached).
@@ -2791,7 +2791,7 @@ dbuf_create(dnode_t *dn, uint8_t level, uint64_t blkid,
 	 * Hold the dn_dbufs_mtx while we get the new dbuf
 	 * in the hash table *and* added to the dbufs list.
 	 * This prevents a possible deadlock with someone
-	 * trying to look up this dbuf before its added to the
+	 * trying to look up this dbuf before it's added to the
 	 * dn_dbufs list.
 	 */
 	mutex_enter(&dn->dn_dbufs_mtx);
@@ -3185,7 +3185,7 @@ dbuf_hold_impl_arg(struct dbuf_hold_arg *dh)
 	ASSERT(dh->dh_db->db_buf == NULL || arc_referenced(dh->dh_db->db_buf));
 
 	/*
-	 * If this buffer is currently syncing out, and we are are
+	 * If this buffer is currently syncing out, and we are
 	 * still referencing it from db_data, we need to make a copy
 	 * of it in case we decide we want to dirty it again in this txg.
 	 */
@@ -3666,7 +3666,7 @@ dbuf_check_blkptr(dnode_t *dn, dmu_buf_impl_t *db)
 		/*
 		 * This buffer was allocated at a time when there was
 		 * no available blkptrs from the dnode, or it was
-		 * inappropriate to hook it in (i.e., nlevels mis-match).
+		 * inappropriate to hook it in (i.e., nlevels mismatch).
 		 */
 		ASSERT(db->db_blkid < dn->dn_phys->dn_nblkptr);
 		ASSERT(db->db_parent == NULL);