affs: Fix memory leaks

affs: Fix memory leaks

The node structure reference is being allocated but not freed if it
reaches the end of the function. If any of the hooks had returned
a non-zero value, then node would have been copied in to the context
reference, but otherwise node is not stored and should be freed.

Similarly, the call to grub_affs_create_node() replaces the allocated
memory in node with a newly allocated structure, leaking the existing
memory pointed by node.

Finally, when dir->parent is set, then we again replace node with newly
allocated memory, which seems unnecessary when we copy in the values
from dir->parent immediately after.

Fixes: CID 73759
Signed-off-by: Darren Kenny <darren.kenny@oracle.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>