mgcp: Use #pragma once instead of a possible clashing #ifdef

The filename is mgcp_internal.h but the define refers to MGCP_DATA.
Avoid having a potential clash by using the #pragma once option.

openbsc/include/openbsc/mgcp_internal.h

@@ -20,8 +20,7 @@
  *
  */
 
-#ifndef OPENBSC_MGCP_DATA_H
-#define OPENBSC_MGCP_DATA_H
+#pragma once
 
 #include <osmocom/core/select.h>
 
@@ -213,4 +212,3 @@ enum {
 
 #define MGCP_DUMMY_LOAD 0x23
 
-#endif