Properly unlock sleep in destructor of drivers

Unlock sleep in CAN and SerialBase. This prevents deep sleep from
staying locked if these objects are destroyed without first clearing
the callbacks.

drivers/CAN.cpp

@@ -46,6 +46,11 @@ CAN::CAN(PinName rd, PinName td, int hz) : _can(), _irq() {
 
 CAN::~CAN() {
     // No lock needed in destructor
+
+    // Detaching interrupts releases the sleep lock if it was locked
+    for (int irq = 0; irq < IrqCnt; irq++) {
+        attach(NULL, (IrqType)irq);
+    }
     can_irq_free(&_can);
     can_free(&_can);
 }

drivers/SerialBase.cpp

@@ -133,6 +133,16 @@ void SerialBase:: unlock() {
     // Stub
 }
 
+SerialBase::~SerialBase()
+{
+    // No lock needed in destructor
+
+    // Detaching interrupts releases the sleep lock if it was locked
+    for (int irq = 0; irq < IrqCnt; irq++) {
+        attach(NULL, (IrqType)irq);
+    }
+}
+
 #if DEVICE_SERIAL_FC
 void SerialBase::set_flow_control(Flow type, PinName flow1, PinName flow2) {
     lock();

drivers/SerialBase.h

@@ -241,8 +241,7 @@ protected:
 
 protected:
     SerialBase(PinName tx, PinName rx, int baud);
-    virtual ~SerialBase() {
-    }
+    virtual ~SerialBase();
 
     int _base_getc();
     int _base_putc(int c);