Change quote style for single char in sam too

Signed-off-by: Patrick Roncagliolo <ronca.pat@gmail.com>

hardware/arduino/sam/cores/arduino/Print.cpp

@@ -242,7 +242,7 @@ size_t Print::printFloat(double number, uint8_t digits)
 
   // Print the decimal point, but only if there are digits beyond
   if (digits > 0) {
-    n += print("."); 
+    n += print('.'); 
   }
 
   // Extract digits from the remainder one at a time