fix spelling errors detected by lintian

Change-Id: I381618eb55cc513cfa9c2e384c27cead0935c8bf
diff --git a/src/gsm_rlcmac.h b/src/gsm_rlcmac.h
index 2ad1937..a4750e8 100644
--- a/src/gsm_rlcmac.h
+++ b/src/gsm_rlcmac.h
@@ -1602,8 +1602,8 @@
 
 typedef struct
 {
-  guint8 Exist_G_RNTI_extention;
-  guint8  G_RNTI_extention;
+  guint8 Exist_G_RNTI_extension;
+  guint8  G_RNTI_extension;
   guint8 Exist_AdditionsR8;
   PCCF_AdditionsR8_t AdditionsR8;
 } PCCF_AdditionsR5_t;