hypfs: avoid effectively open-coding xzalloc_array()

hypfs: avoid effectively open-coding xzalloc_array()

There is a difference in generated code: xzalloc_bytes() forces
SMP_CACHE_BYTES alignment. I think we not only don't need this here, but
actually don't want it.

To avoid the need to add a cast, do away with the only forward-declared
struct hypfs_dyndata.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Juergen Gross <jgross@suse.com>