Fix typo in configuration

Change duplicate of MBEDTLS_ECDH_GEN_PUBLIC_ALT to
MBEDTLS_ECDH_COMPUTE_SHARED_ALT
diff --git a/include/mbedtls/config.h b/include/mbedtls/config.h
index a151f77..a6003b7 100644
--- a/include/mbedtls/config.h
+++ b/include/mbedtls/config.h
@@ -295,7 +295,7 @@
 //#define MBEDTLS_AES_ENCRYPT_ALT
 //#define MBEDTLS_AES_DECRYPT_ALT
 //#define MBEDTLS_ECDH_GEN_PUBLIC_ALT
-//#define MBEDTLS_ECDH_GEN_PUBLIC_ALT
+//#define MBEDTLS_ECDH_COMPUTE_SHARED_ALT
 
 /**
  * \def MBEDTLS_ECP_INTERNAL_ALT