cudaPackages.setupCudaHook: always set return explicitly

On NixOS, the the return status is that of the last command executed within the function or script.

When we're doing tests immediately before the return, the value you end up returning might not be what you want.

pkgs/development/cuda-modules/setup-hooks/setup-cuda-hook.sh

@@ -24,8 +24,8 @@ extendcudaHostPathsSeen() {
     (( "${NIX_DEBUG:-0}" >= 1 )) && echo "extendcudaHostPathsSeen $1" >&2
 
     local markerPath="$1/nix-support/include-in-cudatoolkit-root"
-    [[ ! -f "${markerPath}" ]] && return
-    [[ -v cudaHostPathsSeen[$1] ]] && return
+    [[ ! -f "${markerPath}" ]] && return 0
+    [[ -v cudaHostPathsSeen[$1] ]] && return 0
 
     cudaHostPathsSeen["$1"]=1
 
@@ -33,7 +33,7 @@ extendcudaHostPathsSeen() {
     local cudaOutputName
     read -r cudaOutputName < "$markerPath"
 
-    [[ -z "$cudaOutputName" ]] && return
+    [[ -z "$cudaOutputName" ]] && return 0
 
     local oldPath="${cudaOutputToPath[$cudaOutputName]-}"
     [[ -n "$oldPath" ]] && echo "extendcudaHostPathsSeen: warning: overwriting $cudaOutputName from $oldPath to $1" >&2
@@ -59,7 +59,7 @@ setupCUDAToolkitCompilers() {
     echo Executing setupCUDAToolkitCompilers >&2
 
     if [[ -n "${dontSetupCUDAToolkitCompilers-}" ]] ; then
-        return
+        return 0
     fi
 
     # Point NVCC at a compatible compiler
@@ -99,7 +99,7 @@ preConfigureHooks+=(setupCUDAToolkitCompilers)
 propagateCudaLibraries() {
     (( "${NIX_DEBUG:-0}" >= 1 )) && echo "propagateCudaLibraries: cudaPropagateToOutput=$cudaPropagateToOutput cudaHostPathsSeen=${!cudaHostPathsSeen[*]}" >&2
 
-    [[ -z "${cudaPropagateToOutput-}" ]] && return
+    [[ -z "${cudaPropagateToOutput-}" ]] && return 0
 
     mkdir -p "${!cudaPropagateToOutput}/nix-support"
     # One'd expect this should be propagated-bulid-build-deps, but that doesn't seem to work