run-qemu-robot-test: fix shellcheck error

Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
Change-Id: I1614370835908b4537caed70907d90a8affefed1
diff --git a/run-qemu-robot-test.sh b/run-qemu-robot-test.sh
index 05fb359..a5c032b 100755
--- a/run-qemu-robot-test.sh
+++ b/run-qemu-robot-test.sh
@@ -114,7 +114,7 @@
                                 --env QEMU_BIN="${QEMU_BIN}" \
                                 --env MACHINE="${MACHINE}" \
                                 --workdir "${OBMC_BUILD_DIR}"           \
-                                --volume "${UPSTREAM_WORKSPACE}":"${OBMC_BUILD_DIR}:ro" \
+                                --volume "${UPSTREAM_WORKSPACE}:${OBMC_BUILD_DIR}:ro" \
                                 --tty \
                                 "${DOCKER_IMG_NAME}" "${OBMC_BUILD_DIR}"/boot-qemu-test.exp)