stdenv: fix SC2242

exit -1 == exit 255 but we don't have a reason to use 255

In pkgs/stdenv/generic/setup.sh line 518:
    (( hostOffset <= targetOffset )) || exit -1
                                             ^-- SC2242 (error): Can only exit with status 0-255. Other data should be wri
tten to stdout/stderr.

pkgs/stdenv/generic/setup.sh

@@ -515,7 +515,7 @@ findInputs() {
     local -r targetOffset="$3"
 
     # Sanity check
-    (( hostOffset <= targetOffset )) || exit -1
+    (( hostOffset <= targetOffset )) || exit 1
 
     local varVar="${pkgAccumVarVars[hostOffset + 1]}"
     local varRef="$varVar[$((targetOffset - hostOffset))]"
@@ -644,7 +644,7 @@ activatePackage() {
     local -r targetOffset="$3"
 
     # Sanity check
-    (( hostOffset <= targetOffset )) || exit -1
+    (( hostOffset <= targetOffset )) || exit 1
 
     if [ -f "$pkg" ]; then
         source "$pkg"