* disk/ieee1275/nand.c (grub_nand_iterate): Return
grub_devalias_iterate() result instead of unconditional 0.
* disk/ieee1275/ofdisk.c (grub_ofdisk_iterate): Likewise.
Also, capture hook return value, either directly or via
grub_children_iterate(), and propagate to caller.
* include/grub/ieee1275/ieee1275.h (grub_devalias_iterate,
grub_children_iterate): Return value is now 'int' instead of
'grub_err_t'.
* kern/ieee1275/openfw.c (grub_children_iterate): Fix to behave
like a proper iterator, stopping when hooks return non-zero.
(grub_devalias_iterate): Likewise.