Fix warnings

Author: facchinm

cores/arduino/Serial.cpp

@@ -93,7 +93,7 @@ size_t UART::write(const uint8_t* c, size_t len) {
 	};
 
 	while ( p < end ) {
-		size_t _len = end - p < WRITE_BUFF_SZ ? len % WRITE_BUFF_SZ : WRITE_BUFF_SZ;
+		size_t _len = (size_t)(end - p) < WRITE_BUFF_SZ ? len % WRITE_BUFF_SZ : WRITE_BUFF_SZ;
 		p += _write_block(p, _len);
 	}
 

variants/ARDUINO_NANO33BLE/variant.cpp

@@ -89,7 +89,7 @@ void initVariant() {
 #endif
   };
 
-  for (int i = 0; i < (sizeof(PWM)/sizeof(PWM[0])); i++) {
+  for (unsigned int i = 0; i < (sizeof(PWM)/sizeof(PWM[0])); i++) {
     PWM[i]->ENABLE = 0;
     PWM[i]->PSEL.OUT[0] = 0xFFFFFFFFUL;
   }