Update install_libtorch.sh

Fix check of libtorch.zip

Author: QuantumMisaka

toolchain/scripts/stage4/install_libtorch.sh

@@ -46,8 +46,8 @@ case "${with_libtorch}" in
     if verify_checksums "${install_lock_file}"; then
       echo "${filename} is already installed, skipping it."
     else
-        if [ -f ${archive_file} ]; then
-            echo "${archive_file} is found"
+        if [ -f ${filename} ]; then
+            echo "${filename} is found"
         else
             # download from pytorch.com and checksum
             url=https://download.pytorch.org/libtorch/cpu/${archive_file}