We give a correct expression for C4 in the above paper. To be more precise, we should delete the higher-order (HO) term with (λ/δg)2 in C4. This HO term was finally ignored because of its small value in the paper. The correction therefore does not change the main results of the paper. For C4 of Eq. (29), we should delete the (λ/δg)2 term. Namely, the correct expression of C4 of Eq. (29) is given as (Formula presented.) In accordance with the revision of C4, we should delete a sentence which starts from 5th line from top in the right side of p. 1029, i.e., “Note that, from now on, we ignore the second term of the right-hand side of C4, i.e., (3/32) (λ/δg)2[(λ/∆) - λ/(|Hex| + ∆)]2, because this term is considered to be sufficiently smaller than the first term with only (λ/∆)2 and [λ/(|Hex| - ∆)]2 due to δg > |λ|.”.