Fix FTBFS with GCC6

Signed-off-by: Slávek Banko <slavek.banko@axis.cz>
(cherry picked from commit dd20ae0d5b)

src/electronics/port.cpp

@@ -244,13 +244,13 @@ const int IRQ_MODE_BIT = 1 << 20; // Controls if pin 10 (Ack) causes interrupts
 const int INPUT_MODE_BIT = 1 << 21; // Controls if the data pins are input or output
 const int ALWAYS_INPUT_PINS = ParallelPort::STATUS_PINS;
 
-const int IOCTL_REG_READ[3] = {
+const unsigned int IOCTL_REG_READ[3] = {
 	PPRDATA,
 	PPRSTATUS,
 	PPRCONTROL,
 };
 
-const int IOCTL_REG_WRITE[3] = {
+const unsigned int IOCTL_REG_WRITE[3] = {
 	PPWDATA,
 	0,
 	PPWCONTROL,