fix a typo in comment (scroll-tech#1351)

### Description

Fix a typo found by another community developer

### Issue Link

N/A

### Type of change

- [ ] Bug fix (non-breaking change which fixes an issue)
- [ ] New feature (non-breaking change which adds functionality)
- [ ] Breaking change (fix or feature that would cause existing
functionality to not work as expected)
- [ ] This change requires a documentation update

### Contents

N/A


### How Has This Been Tested?

N/A

zkevm-circuits/src/evm_circuit/util/math_gadget/mul_add_words.rs

@@ -24,16 +24,16 @@ use halo2_proofs::{
 ///   t2 = a0 * b2 + a2 * b0 + a1 * b1, contribute to above 128 bit
 ///   t3 = a0 * b3 + a3 * b0 + a2 * b1 + a1 * b2, contribute to above 192 bit
 ///
-/// so t0 ~ t1 include all contributions to the low 256-bit of product, with
+/// so t0 ~ t3 include all contributions to the low 256-bit of product, with
 /// a maximum 68-bit radix (the part higher than 256-bit), denoted as carry_hi
 /// Similarly, we define carry_lo as the radix of contributions to the low
 /// 128-bit of the product.
 /// We can slightly relax the constraint of carry_lo/carry_hi to 72-bit and
 /// allocate 9 bytes for them each
 ///
 /// Finally we just prove:
-///   t0 + t1 * 2^64 = <low 128 bit of product> + carry_lo
-///   t2 + t3 * 2^64 + carry_lo = <high 128 bit of product> + carry_hi
+///   t0 + t1 * 2^64 = <low 128 bit of product> + carry_lo * 2^128
+///   t2 + t3 * 2^64 + carry_lo = <high 128 bit of product> + carry_hi * 2^128
 ///
 /// Last, we sum the parts that are higher than 256-bit in the multiplication
 /// into overflow