Fix some misspellings

Some files contained English misspellings or math issues (`lamba`
instead of `lambda`).

src/scalar_impl.h

@@ -90,11 +90,11 @@ static void secp256k1_scalar_split_lambda_verify(const secp256k1_scalar *r1, con
 #endif
 
 /*
- * Both lambda and beta are primitive cube roots of unity.  That is lamba^3 == 1 mod n and
+ * Both lambda and beta are primitive cube roots of unity.  That is lambda^3 == 1 mod n and
  * beta^3 == 1 mod p, where n is the curve order and p is the field order.
  *
  * Furthermore, because (X^3 - 1) = (X - 1)(X^2 + X + 1), the primitive cube roots of unity are
- * roots of X^2 + X + 1.  Therefore lambda^2 + lamba == -1 mod n and beta^2 + beta == -1 mod p.
+ * roots of X^2 + X + 1.  Therefore lambda^2 + lambda == -1 mod n and beta^2 + beta == -1 mod p.
  * (The other primitive cube roots of unity are lambda^2 and beta^2 respectively.)
  *
  * Let l = -1/2 + i*sqrt(3)/2, the complex root of X^2 + X + 1. We can define a ring

src/util.h

@@ -232,7 +232,7 @@ static SECP256K1_INLINE void secp256k1_memclear(void *ptr, size_t len) {
      *    As best as we can tell, this is sufficient to break any optimisations that
      *    might try to eliminate "superfluous" memsets.
      * This method is used in memzero_explicit() the Linux kernel, too. Its advantage is that it
-     * is pretty efficient, because the compiler can still implement the memset() efficently,
+     * is pretty efficient, because the compiler can still implement the memset() efficiently,
      * just not remove it entirely. See "Dead Store Elimination (Still) Considered Harmful" by
      * Yang et al. (USENIX Security 2017) for more background.
      */