Tighten secp256k1_fe_mul_inner's VERIFY_BITS checks

These changes bring the checks to the same values used at the corresponding positions in secp256k1_fe_sqr_inner.

Author: roconnor-blockstream

src/field_5x52_int128_impl.h

@@ -89,11 +89,11 @@ SECP256K1_INLINE static void secp256k1_fe_mul_inner(uint64_t *r, const uint64_t
     secp256k1_u128_accum_mul(&d, a2, b[3]);
     secp256k1_u128_accum_mul(&d, a3, b[2]);
     secp256k1_u128_accum_mul(&d, a4, b[1]);
-    VERIFY_BITS_128(&d, 115);
+    VERIFY_BITS_128(&d, 114);
     /* [d t4+(tx<<48) t3 0 0 c] = [p8 0 0 p5 p4 p3 0 0 p0] */
     u0 = secp256k1_u128_to_u64(&d) & M; secp256k1_u128_rshift(&d, 52);
     VERIFY_BITS(u0, 52);
-    VERIFY_BITS_128(&d, 63);
+    VERIFY_BITS_128(&d, 62);
     /* [d u0 t4+(tx<<48) t3 0 0 c] = [p8 0 0 p5 p4 p3 0 0 p0] */
     /* [d 0 t4+(tx<<48)+(u0<<52) t3 0 0 c] = [p8 0 0 p5 p4 p3 0 0 p0] */
     u0 = (u0 << 4) | tx;