deb: install openbsc.pc

Previously openbsc.pc was generated but not installed as part of
openbsc-dev.

Change-Id: I5472a8fe74a81b98598fbdb688db778cb7d09e62
diff --git a/debian/openbsc-dev.install b/debian/openbsc-dev.install
index 398321a..0c05545 100644
--- a/debian/openbsc-dev.install
+++ b/debian/openbsc-dev.install
@@ -1,3 +1,4 @@
 openbsc/include/openbsc/gsm_data_shared.h usr/src/osmocom/openbsc/openbsc/include/openbsc/
 openbsc/include/openbsc/common_cs.h usr/src/osmocom/openbsc/openbsc/include/openbsc/
 openbsc/src/libcommon/gsm_data_shared.c usr/src/osmocom/openbsc/openbsc/src/libcommon/
+usr/lib/*/pkgconfig/openbsc.pc