super1: separate to version of _avail_space1().

super1: separate to version of _avail_space1().

_avail_space1() is calls from both avail_space1() and validate_geometry1()
and does slightly different things.

The partial code sharing doesn't really help.  In particularly the
responsibility for setting the size of the array is currently
confused.

So duplicate the code into the two locations - one where 'super' is
always NULL (validate_geometry1) and one where it is never NULL
(avail_space1), and simplify.

No behaviour change - just code re-organisation.

Signed-off-by: NeilBrown <neilb@suse.de>