fat: fix non-atomic NFS i_pos read

fat_encode_fh(struct inode *inode, __u32 *fh, int *lenp, struct inode *parent)

{

	int len = *lenp;

	u32 ipos_h, ipos_m, ipos_l;

	struct msdos_sb_info *sbi = MSDOS_SB(inode->i_sb);

	loff_t i_pos;

	if (len < 5) {

		*lenp = 5;

		return 255; /* no room */

	}

	ipos_h = MSDOS_I(inode)->i_pos >> 8;

	ipos_m = (MSDOS_I(inode)->i_pos & 0xf0) << 24;

	ipos_l = (MSDOS_I(inode)->i_pos & 0x0f) << 28;

	i_pos = fat_i_pos_read(sbi, inode);

	*lenp = 5;

	fh[0] = inode->i_ino;

	fh[1] = inode->i_generation;

	fh[2] = ipos_h;

	fh[3] = ipos_m | MSDOS_I(inode)->i_logstart;

	fh[4] = ipos_l;

	fh[2] = i_pos >> 8;

	fh[3] = ((i_pos & 0xf0) << 24) | MSDOS_I(inode)->i_logstart;

	fh[4] = (i_pos & 0x0f) << 28;

	if (parent)

		fh[4] |= MSDOS_I(parent)->i_logstart;

	return 3;