VENV: Install dependencies with absolute path

Switches from using relative path for installing TF-M python deps to
using the absolute path.

Change-Id: I1110dcaffc0bf507f2675b4de43b03372f6113e2
Signed-off-by: Matthew Dalzell <matthew.dalzell@arm.com>
diff --git a/clone.sh b/clone.sh
index 2ee3308..e3b3a8c 100755
--- a/clone.sh
+++ b/clone.sh
@@ -108,7 +108,7 @@
     exit 1
 fi
 
-pip install --no-deps ../trusted-firmware-m/
+pip install --no-deps ${WORKSPACE}/${TFM_NAME}
 
 # Dependency projects
 TFM_TESTS_PROJECT="${TFM_TESTS_URL:-}"