Port: Make getAddrRanges const

This patch makes getAddrRanges const throughout the code base. There
is no reason why it should not be, and making it const prevents adding
any unintentional side-effects.

src/dev/io_device.cc

@@ -58,7 +58,7 @@ PioPort::recvAtomic(PacketPtr pkt)
 }
 
 AddrRangeList
-PioPort::getAddrRanges()
+PioPort::getAddrRanges() const
 {
     return device->getAddrRanges();
 }
@@ -106,7 +106,7 @@ BasicPioDevice::BasicPioDevice(const Params *p)
 {}
 
 AddrRangeList
-BasicPioDevice::getAddrRanges()
+BasicPioDevice::getAddrRanges() const
 {
     assert(pioSize != 0);
     AddrRangeList ranges;