Fix fail path in zfs_znode_alloc

Fix fail path in zfs_znode_alloc

When sa_bulk_lookup() fails, unlock_new_inode() will spit out a WARNING. It
will also recursive deadlock on ZFS_OBJ_HOLD_ENTER in zfs_zinactive().

Since we never call insert_inode_locked in fail path, I_NEW is never set, the
inode is never hashed. So unlock_new_inode() can be safely remove it.

We set z_sa_hdl to NULL in fail path so that iput path will stop at
zfs_inactive() without entering zfs_zinactive(). This way we can avoid the
deadlock and prevent double sa_handle_destroy().

Signed-off-by: Chunwei Chen <david.chen@osnexus.com>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Issue #3899