Fix docs for EVP_EncryptUpdate and EVP_DecryptUpdate

Fixes #4775
[skip ci]
Reviewed-by: NViktor Dukhovni <viktor@openssl.org>
Reviewed-by: NMatt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/4776)

doc/man3/EVP_EncryptInit.pod

@@ -61,13 +61,13 @@ EVP_enc_null
  int EVP_EncryptInit_ex(EVP_CIPHER_CTX *ctx, const EVP_CIPHER *type,
                         ENGINE *impl, unsigned char *key, unsigned char *iv);
  int EVP_EncryptUpdate(EVP_CIPHER_CTX *ctx, unsigned char *out,
-                       int *outl, unsigned char *in, int inl);
+                       int *outl, const unsigned char *in, int inl);
  int EVP_EncryptFinal_ex(EVP_CIPHER_CTX *ctx, unsigned char *out, int *outl);
 
  int EVP_DecryptInit_ex(EVP_CIPHER_CTX *ctx, const EVP_CIPHER *type,
                         ENGINE *impl, unsigned char *key, unsigned char *iv);
  int EVP_DecryptUpdate(EVP_CIPHER_CTX *ctx, unsigned char *out,
-                       int *outl, unsigned char *in, int inl);
+                       int *outl, const unsigned char *in, int inl);
  int EVP_DecryptFinal_ex(EVP_CIPHER_CTX *ctx, unsigned char *outm, int *outl);
 
  int EVP_CipherInit_ex(EVP_CIPHER_CTX *ctx, const EVP_CIPHER *type,