grub_util_fd_strerror when using grub_util_fd_*.
(grub_util_fd_open_device): Likewise.
(grub_util_biosdisk_read): Likewise.
(grub_util_biosdisk_write): Likewise.
* grub-core/kern/emu/hostdisk_unix.c (grub_util_fd_open): New function.
(grub_util_fd_strerror): Likewise.
(grub_util_fd_sync): Likewise.
(grub_util_fd_close): Likewise.
* grub-core/kern/emu/hostdisk_windows.c (grub_util_fd_sync): Likewise.
(grub_util_fd_close): Likewise.
(grub_util_fd_strerror): Likewise.
* include/grub/emu/hostdisk.h (grub_util_fd_close): Make into real
function proto rather than macro.
(grub_util_fd_sync): Likewise.
(grub_util_fd_open): Likewise.
(grub_util_fd_strerror): New proto.
