debian/control: Add build dependency to libusrp-dev

Change-Id: I9593c9e45d304b7ffc94474e94450da418838513
diff --git a/debian/control b/debian/control
index 4705e64..b7e499e 100644
--- a/debian/control
+++ b/debian/control
@@ -12,6 +12,7 @@
                libboost-all-dev,
                libfftw3-dev,
                libtalloc-dev,
+               libusrp-dev,
                libosmocore-dev (>= 0.10.0)
 Standards-Version: 3.9.6
 Vcs-Browser: http://cgit.osmocom.org/osmo-trx