super1: make aread/awrite always use an aligned buffer.

super1: make aread/awrite always use an aligned buffer.

A recently change to write_bitmap1 meant awrite would sometimes
write from a non-aligned buffer which of course break.

So change awrite (and aread) to always use their own aligned
buffer to ensure safety.

Reported-by: Alexander Lyakas <alex.bolshoy@gmail.com>
Signed-off-by: NeilBrown <neilb@suse.de>