warning cleanup: add missing return statements

Add missing default return values to functions returning non-void.
Also remove spuperfluous 'return;' statements at the end of functions.

Signed-off-by: Luca Burelli <l.burelli@arduino.cc>

Author: pillo79

libraries/Camera/src/camera.cpp

@@ -31,12 +31,16 @@ uint32_t FrameBuffer::getBufferSize() {
 	if (this->vbuf) {
 		return this->vbuf->bytesused;
 	}
+
+	return 0;
 }
 
 uint8_t *FrameBuffer::getBuffer() {
 	if (this->vbuf) {
 		return this->vbuf->buffer;
 	}
+
+	return NULL;
 }
 
 Camera::Camera() : vdev(NULL), byte_swap(false), yuv_to_gray(false) {

libraries/SocketWrapper/SocketHelpers.cpp

@@ -163,7 +163,6 @@ void NetworkInterface::config(const IPAddress ip, const IPAddress dns_server,
 	setDnsServerIP(dns_server);
 	setGatewayIP(gateway);
 	setSubnetMask(subnet);
-	return;
 }
 
 void NetworkInterface::setLocalIP(const IPAddress ip) {
@@ -175,7 +174,6 @@ void NetworkInterface::setLocalIP(const IPAddress ip) {
 		return;
 	}
 	LOG_INF("Local IP address set: %s", ip.toString().c_str());
-	return;
 }
 
 void NetworkInterface::setSubnetMask(const IPAddress subnet) {

libraries/WiFi/src/WiFi.cpp

@@ -84,6 +84,7 @@ int WiFiClass::status() {
 
 int8_t WiFiClass::scanNetworks() {
 	// TODO: borrow code from mbed core for scan results handling
+	return 0;
 }
 
 char *WiFiClass::SSID() {