staging/lustre: Convert cfs_str2num_check to use kstrtoul

cfs_str2num_check(char *str, int nob, unsigned *num,

		  unsigned min, unsigned max)

{

	char	*endp;

	int rc;

	str = cfs_trimwhite(str);

	*num = simple_strtoul(str, &endp, 0);

	if (endp == str)

		return 0;

	for (; endp < str + nob; endp++) {

		if (!isspace(*endp))

	rc = kstrtouint(str, 10, num);

	if (rc)

		return 0;

	}

	return (*num >= min && *num <= max);

}