getinfo_super now clears the 'info' structure before filling it in.

getinfo_super now clears the 'info' structure before filling it in.

Some code currently clears 'info' before calling getinfo_super,
some code doesn't.

To be consistent, change it so no caller ever clears 'info',
but ever getinfo_super function must clear it.

Note that ->raid_disk may be meaningful if that 'map' is passed
non-NULL.  In that case it is copied out before the structure
is zeroed.

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