include: Switch to #pragma once pattern

Signed-off-by: Sylvain Munaut <tnt@246tNt.com>
diff --git a/include/osmocom/gsm/gan.h b/include/osmocom/gsm/gan.h
index ab4c1e4..6f2b535 100644
--- a/include/osmocom/gsm/gan.h
+++ b/include/osmocom/gsm/gan.h
@@ -1,9 +1,6 @@
-#ifndef _OSMO_GSM_GAN_H
-#define  _OSMO_GSM_GAN_H
+#pragma once
 
 #include <osmocom/core/utils.h>
 
 extern const struct value_string gan_msgt_vals[];
 static const struct value_string gan_pdisc_vals[];
-
-#endif