gpsd.bbappend: Use the same SRC_URI definition as the main recipe

These variables may change in updates either in poky repo or
meta-openembedded, using directly the variable instead of the
static string name make it more failsafe to future upgrades.

recipes-connectivity/gpsd/gpsd_3.17.bbappend

@@ -3,7 +3,7 @@ SRC_URI =+ " \
             git://git.netmodule.intranet/nmsw/gpsd.git;protocol=ssh;user=gitea;branch=imu-integration \
             file://60-ublox-neo.rules \ 
             "
-SRC_URI_remove = "https://download.savannah.gnu.org/releases/gpsd/gpsd-3.17.tar.gz"
+SRC_URI_remove = "${SAVANNAH_GNU_MIRROR}/${BPN}/${BP}.tar.gz"
 
 # overwrite default gpsd.service file with our configuration
 SRCREV = "${AUTOREV}"