handorer.h: Fix compilation with gcc-10

/usr/bin/ld: bsc_subscr_conn_fsm.o:/home/laforge/projects/git/osmo-bsc/src/osmo-bsc/../../include/osmocom/bsc/handover.h:26: multiple definition of `mr'; abis_rsl.o:/home/laforge/projects/git/osmo-bsc/src/osmo-bsc/../../include/osmocom/bsc/handover.h:26: first defined here

See also https://alioth-lists.debian.net/pipermail/debian-mobcom-maintainers/Week-of-Mon-20200413/000649.html

Change-Id: Ic21af84f2a6de48d220940f30dad02a0e7683ce8
diff --git a/include/osmocom/bsc/handover.h b/include/osmocom/bsc/handover.h
index b00ee60..d22ac86 100644
--- a/include/osmocom/bsc/handover.h
+++ b/include/osmocom/bsc/handover.h
@@ -23,7 +23,7 @@
 struct gsm_lchan;
 struct gsm_bts;
 struct gsm_subscriber_connection;
-struct gsm_meas_rep mr;
+struct gsm_meas_rep;
 
 enum handover_result {
 	HO_RESULT_OK,