zfs userspace dumps core when used on ZVOLs

zfs userspace dumps core when used on ZVOLs

If you try to get the userspace, groupspace or projectspace on a ZVOL,
the generated error results in passing EINVAL to
zfs_standard_error_fmt() when we should return a specific error to
inform the user that those properties aren't available on volumes.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed by: Tom Caputi <tcaputi@datto.com>
Signed-off-by: loli10K <ezomori.nozomu@gmail.com>
Closes #8279