Update comments to reflect Stream functions changed from private to protected

These functions were changed from private to protected but the comments were not updated at that time.

In conjunction with equivalent pull requests to Arduino AVR Boards and Arduino SAMD Boards, solves arduino#6146.

Author: per1234

cores/arduino/Stream.cpp

@@ -27,7 +27,7 @@
 
 #define PARSE_TIMEOUT 1000  // default number of milli-seconds to wait
 
-// private method to read stream with timeout
+// protected method to read stream with timeout
 int Stream::timedRead()
 {
   int c;
@@ -39,7 +39,7 @@ int Stream::timedRead()
   return -1;     // -1 indicates timeout
 }
 
-// private method to peek stream with timeout
+// protected method to peek stream with timeout
 int Stream::timedPeek()
 {
   int c;

cores/arduino/Stream.h

@@ -51,8 +51,8 @@ class Stream : public Print
   protected:
     unsigned long _timeout;      // number of milliseconds to wait for the next char before aborting timed read
     unsigned long _startMillis;  // used for timeout measurement
-    int timedRead();    // private method to read stream with timeout
-    int timedPeek();    // private method to peek stream with timeout
+    int timedRead();    // read stream with timeout
+    int timedPeek();    // peek stream with timeout
     int peekNextDigit(LookaheadMode lookahead, bool detectDecimal); // returns the next numeric digit in the stream or -1 if timeout
 
   public: