Fix zfs_znode_sa_init() panic by updating ZFS_OBJ_MUTEX()

The time at which a zp's z_zfsvfs is assigned was changed in
upstream here:

https://github.com/illumos/illumos-gate/commit/b5fca8f855054d167d04d3b4de5210c83ed2083c

Although we had already merged in most of that change, we had
neglected to update the definition of ZFS_OBJ_MUTEX() to the new
two-argument version. Yet, when actually invoking the macro, we
were supplying two arguments.

In an attempt to reconcile the discrepancy, the panic was
introduced by

https://github.com/openzfsonosx/zfs/commit/8881f60a486ddb0295033ac01d36758b9594d128

which erroneously reverted the new code where the two-argument
version was used, rather than updating ZFS_OBJ_MUTEX() to the new
two-argument version.

This results in panic because ZFS_OBJ_MUTEX() happens to be used
before zp->z_zfsvfs has been assigned, while the one-argument
version of ZFS_OBJ_MUTEX() expects to be able to retrieve the
zfsvfs from the zp.