Typo fix

Author: ivankravets

platform.py

@@ -20,7 +20,7 @@ class Espressif8266Platform(PlatformBase):
     def configure_default_packages(self, variables, targets):
         framework = variables.get("pioframework")
         if "arduino" not in framework:
-            self.packages['tool-mkspiffs']['optional'] = "~1.40802.0"
+            self.packages['toolchain-xtensa']['version'] = "~1.40802.0"
         if "buildfs" in targets:
             self.packages['tool-mkspiffs']['optional'] = False
         return PlatformBase.configure_default_packages(