Added include guard to onewire_library.h (raspberrypi#595)

Author: gumpump

pio/onewire/onewire_library/onewire_library.h

@@ -1,3 +1,6 @@
+#ifndef _ONEWIRE_LIBRARY_H
+#define _ONEWIRE_LIBRARY_H
+
 #include "hardware/pio.h"
 #include "hardware/clocks.h"            // for clock_get_hz() in generated header
 #include "onewire_library.pio.h"        // generated by pioasm
@@ -14,4 +17,6 @@ bool ow_init (OW *ow, PIO pio, uint offset, uint gpio);
 void ow_send (OW *ow, uint data);
 uint8_t ow_read (OW *ow);
 bool ow_reset (OW *ow);
-int ow_romsearch (OW *ow, uint64_t *romcodes, int maxdevs, uint command);
+int ow_romsearch (OW *ow, uint64_t *romcodes, int maxdevs, uint command);
+
+#endif