Add error if I2S is not supported by the variant

Author: sandeepmistry

libraries/I2S/src/I2S.h

@@ -107,6 +107,8 @@ class I2SClass : public Stream
 
 #if I2S_INTERFACES_COUNT > 0
 extern I2SClass I2S;
+#else
+#error "I2S is not supported on your board!"
 #endif
 
 #endif