include: Switch to #pragma once pattern

Signed-off-by: Sylvain Munaut <tnt@246tNt.com>
diff --git a/include/osmocom/gprs/protocol/gsm_08_18.h b/include/osmocom/gprs/protocol/gsm_08_18.h
index 3a351ea..529e988 100644
--- a/include/osmocom/gprs/protocol/gsm_08_18.h
+++ b/include/osmocom/gprs/protocol/gsm_08_18.h
@@ -1,5 +1,4 @@
-#ifndef _OSMO_08_18_H
-#define _OSMO_08_18_H
+#pragma once
 
 #include <stdint.h>
 
@@ -140,5 +139,3 @@
 	BSSGP_CAUSE_PROTO_ERR_UNSPEC	= 0x27,
 	BSSGP_CAUSE_PDU_INCOMP_FEAT	= 0x28,
 };
-
-#endif