cosmetic: Fix typo s/TIMSI/TMSI/

Change-Id: I64231311633b64d898625c49fdbf3f816dfbb97a
diff --git a/src/gprs_bssgp_pcu.c b/src/gprs_bssgp_pcu.c
index 5d0a489..7ee2e45 100644
--- a/src/gprs_bssgp_pcu.c
+++ b/src/gprs_bssgp_pcu.c
@@ -191,7 +191,7 @@
 	}
 	req->mi_imsi_present = true;
 
-	/* TIMSI is optional */
+	/* TMSI is optional */
 	req->mi_tmsi_present = false;
 	if (TLVP_PRESENT(tp, BSSGP_IE_TMSI)) {
 		/* Be safe against an evil SGSN - check the length */