Correct Logging macro for pdpctx_timer_start

This commit corrects the Logging macro used in pdpctx_timer_start.

Change-Id: Id4e3a7fb934ed82af8096fda9ddd3f4550e05844
diff --git a/openbsc/src/gprs/gprs_gmm.c b/openbsc/src/gprs/gprs_gmm.c
index 8de3bf7..b30b8d3 100644
--- a/openbsc/src/gprs/gprs_gmm.c
+++ b/openbsc/src/gprs/gprs_gmm.c
@@ -1978,7 +1978,7 @@
 				unsigned int seconds)
 {
 	if (osmo_timer_pending(&pdp->timer))
-		LOGMMCTXP(LOGL_ERROR, pdp->mm, "Starting MM timer %u while old "
+		LOGPDPCTXP(LOGL_ERROR, pdp, "Starting PDP timer %u while old "
 			"timer %u pending\n", T, pdp->T);
 	pdp->T = T;
 	pdp->num_T_exp = 0;