include/hw/or-irq.h: Add missing include guard

The or-irq.h header file is missing the customary guard against
multiple inclusion, which means compilation fails if it gets
included twice. Fix the omission.
Signed-off-by: NPeter Maydell <peter.maydell@linaro.org>
Reviewed-by: NPhilippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: NRichard Henderson <richard.henderson@linaro.org>
Message-id: 20180220180325.29818-11-peter.maydell@linaro.org

include/hw/or-irq.h

@@ -22,6 +22,9 @@
  * THE SOFTWARE.
  */
 
+#ifndef HW_OR_IRQ_H
+#define HW_OR_IRQ_H
+
 #include "hw/irq.h"
 #include "hw/sysbus.h"
 #include "qom/object.h"
@@ -41,3 +44,5 @@ struct OrIRQState {
     bool levels[MAX_OR_LINES];
     uint16_t num_lines;
 };
+
+#endif