Fix few obvious type discrepancies.

	Fix few obvious type discrepancies.

	* grub-core/fs/affs.c (grub_affs_read_file): Use grub_off_t for offset.
	* grub-core/fs/afs.c (grub_afs_read_file): Likewise.
	* grub-core/fs/fshelp.c (grub_fshelp_find_file): Remove leftover
	variable.
	* grub-core/fs/hfs.c (grub_hfs_read_file): Use grub_off_t for offset
	and connected types.
	* grub-core/fs/nilfs2.c (grub_nilfs2_read_file): Use grub_off_t for
	offset.
	(grub_nilfs2_iterate_dir): Use grub_off_t for fpos.
	* grub-core/fs/sfs.c (grub_sfs_read_file): Use grub_off_t for offset.
	* grub-core/fs/ufs.c (grub_ufs_read_file): Use grub_off_t for offset
	and connected types.