OpenZFS 8061 - sa_find_idx_tab can be declared more type-safely

Authored by: Matthew Ahrens <mahrens@delphix.com>
Approved by: Dan McDonald <danmcd@omniti.com>
Reviewed by: George Wilson <george.wilson@delphix.com>
Reviewed by: Chris Williamson <chris.williamson@delphix.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Ported-by: Giuseppe Di Natale <dinatale2@llnl.gov>

sa_find_idx_tab() is declared as taking and returning "void *" parameters.
These can be declared to be the specific types.

OpenZFS-issue: https://www.illumos.org/issues/8061
OpenZFS-commit: openzfs/openzfs@4e64aff
Closes #6017

module/zfs/sa.c

@@ -21,7 +21,7 @@
 
 /*
  * Copyright (c) 2010, Oracle and/or its affiliates. All rights reserved.
- * Copyright (c) 2016 by Delphix. All rights reserved.
+ * Copyright (c) 2013, 2017 by Delphix. All rights reserved.
  * Copyright (c) 2014 Spectra Logic Corporation, All rights reserved.
  */
 
@@ -130,8 +130,8 @@ typedef void (sa_iterfunc_t)(void *hdr, void *addr, sa_attr_type_t,
 
 static int sa_build_index(sa_handle_t *hdl, sa_buf_type_t buftype);
 static void sa_idx_tab_hold(objset_t *os, sa_idx_tab_t *idx_tab);
-static void *sa_find_idx_tab(objset_t *os, dmu_object_type_t bonustype,
-    void *data);
+static sa_idx_tab_t *sa_find_idx_tab(objset_t *os, dmu_object_type_t bonustype,
+    sa_hdr_phys_t *hdr);
 static void sa_idx_tab_rele(objset_t *os, void *arg);
 static void sa_copy_data(sa_data_locator_t *func, void *start, void *target,
     int buflen);
@@ -1498,11 +1498,10 @@ sa_lookup_uio(sa_handle_t *hdl, sa_attr_type_t attr, uio_t *uio)
 }
 #endif
 
-void *
-sa_find_idx_tab(objset_t *os, dmu_object_type_t bonustype, void *data)
+static sa_idx_tab_t *
+sa_find_idx_tab(objset_t *os, dmu_object_type_t bonustype, sa_hdr_phys_t *hdr)
 {
 	sa_idx_tab_t *idx_tab;
-	sa_hdr_phys_t *hdr = (sa_hdr_phys_t *)data;
 	sa_os_t *sa = os->os_sa;
 	sa_lot_t *tb, search;
 	avl_index_t loc;