Use modulo operator in Print::printNumber

Port of @tico-tico’s change in
https://github.com/tico-tico/Arduino/commit/a7454b6b5c59187b95c4224aad87
bb01faa06e85 to SAMD core.

cores/arduino/Print.cpp

@@ -188,7 +188,8 @@ size_t Print::println(const Printable& x)
 
 // Private Methods /////////////////////////////////////////////////////////////
 
-size_t Print::printNumber(unsigned long n, uint8_t base) {
+size_t Print::printNumber(unsigned long n, uint8_t base)
+{
   char buf[8 * sizeof(long) + 1]; // Assumes 8-bit chars plus zero byte.
   char *str = &buf[sizeof(buf) - 1];
 
@@ -198,9 +199,9 @@ size_t Print::printNumber(unsigned long n, uint8_t base) {
   if (base < 2) base = 10;
 
   do {
-    unsigned long m = n;
+    char c = n % base;
     n /= base;
-    char c = m - base * n;
+
     *--str = c < 10 ? c + '0' : c + 'A' - 10;
   } while(n);