msc/signal.h: use #pragma once include guard

Change-Id: I114026808abeff72a3f4f3cb1b84680c116409d4
diff --git a/include/osmocom/msc/signal.h b/include/osmocom/msc/signal.h
index e854a64..f630b27 100644
--- a/include/osmocom/msc/signal.h
+++ b/include/osmocom/msc/signal.h
@@ -19,8 +19,7 @@
  *
  */
 
-#ifndef OPENBSC_SIGNAL_H
-#define OPENBSC_SIGNAL_H
+#pragma once
 
 #include <stdlib.h>
 #include <errno.h>
@@ -99,5 +98,3 @@
 	/* int paging result. Only the ones with > 0 */
 	int paging_result;
 };
-
-#endif