cmake: fix git dependency for version.h creation

Fixes: #63610

Fix a variable spelling mistake which caused a required dependency to
not be set.

Together with this fix, then remove an unneeded CMake cache update.

The `ZEPHYR_GIT_INDEX-NOTFOUND` value is not really useful in this
case as a not set var will also ensure that Zephyr is checked to be
a git repo or not.
And when detected as a git repo, then `ZEPHYR_GIT_INDEX` is set
to correct value.

Signed-off-by: Torsten Rasmussen <[email protected]>

Author: tejlmand

CMakeLists.txt

@@ -511,11 +511,9 @@ endif()
 if(DEFINED BUILD_VERSION)
   set(build_version_argument "-DBUILD_VERSION=${BUILD_VERSION}")
 elseif(NOT ZEPHYR_GIT_INDEX)
-  set(ZEPHYR_GIT_INDEX ZEPHYR_GIT_INDEX-NOTFOUND CACHE PATH
-    "Path to Zephyr git repository index file")
   if(EXISTS ${ZEPHYR_BASE}/.git/index)
-    set(ZEPHYR_GIT_DIR ${ZEPHYR_BASE}/.git/index CACHE PATH
-      "Path to Zephyr git repository index file" FORCE)
+    set(ZEPHYR_GIT_INDEX ${ZEPHYR_BASE}/.git/index CACHE PATH
+      "Path to Zephyr git repository index file")
   elseif(EXISTS ${ZEPHYR_BASE}/.git)
     # Likely a git-submodule. Let's ask git where the real database is located.
     find_package(Git QUIET)
@@ -535,7 +533,7 @@ elseif(NOT ZEPHYR_GIT_INDEX)
           message(WARNING "BUILD_VERSION: git rev-parse warned: ${stderr}")
         endif()
         set(ZEPHYR_GIT_INDEX ${zephyr_git_dir}/index CACHE PATH
-          "Path to Zephyr git repository index file" FORCE)
+          "Path to Zephyr git repository index file")
       endif()
     else()
       message(WARNING "Could not find git installation, "