ESP32: Fix memory leak in crypto functions (#1402)

Author: tekka007

hal/crypto/ESP32/MyCryptoESP32.cpp

@@ -28,6 +28,7 @@ void SHA256(uint8_t *dest, const uint8_t *data, size_t dataLength)
 	mbedtls_md_starts(&ctx);
 	mbedtls_md_update(&ctx, (const unsigned char *)data, dataLength);
 	mbedtls_md_finish(&ctx, dest);
+	mbedtls_md_free(&ctx);
 }
 
 
@@ -42,6 +43,7 @@ void SHA256HMAC(uint8_t *dest, const uint8_t *key, size_t keyLength, const uint8
 	mbedtls_md_hmac_starts(&ctx, (const unsigned char *)key, keyLength);
 	mbedtls_md_hmac_update(&ctx, (const unsigned char *)data, dataLength);
 	mbedtls_md_hmac_finish(&ctx, dest);
+	mbedtls_md_free(&ctx);
 }
 
 // ESP32 AES128 CBC