Illumos #3522

3522 zfs module should not allow uninitialized variables
Reviewed by: Sebastien Roy <seb@delphix.com>
Reviewed by: Adam Leventhal <ahl@delphix.com>
Reviewed by: Matthew Ahrens <mahrens@delphix.com>
Approved by: Garrett D'Amore <garrett@damore.org>

References:
  https://www.illumos.org/issues/3522
  illumos/illumos-gate@d5285cae91

Ported-by: Richard Yao <ryao@gentoo.org>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>

Porting notes:

1. ZFSOnLinux had already addressed many of these issues because of
   its use of -Wall. However, the manner in which they were addressed
   differed. The illumos fixes replace the ones previously made in
   ZFSOnLinux to reduce code differences.

2. Part of the upstream patch made a small change to arc.c that might
   address zfsonlinux/zfs#1334.

3. The initialization of aclsize in zfs_log_create() differs because
   vsecp is a NULL pointer on ZFSOnLinux.

4. The changes to zfs_register_callbacks() were dropped because it
   has diverged and needs to be resynced.

module/zfs/dmu_objset.c

@@ -1198,7 +1198,8 @@ dmu_objset_userquota_get_ids(dnode_t *dn, boolean_t before, dmu_tx_t *tx)
 	objset_t *os = dn->dn_objset;
 	void *data = NULL;
 	dmu_buf_impl_t *db = NULL;
-	uint64_t *user = NULL, *group = NULL;
+	uint64_t *user = NULL;
+	uint64_t *group = NULL;
 	int flags = dn->dn_id_flags;
 	int error;
 	boolean_t have_spill = B_FALSE;