Use '-f' option to point to the .gitmodules file

'git config' has a '-f' option that takes the file to parse.
Using it rather than the environment variable seems more logical
and simplified.
Signed-off-by: NImran M Yousuf <imyousuf@smartitengineering.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

git-submodule.sh

@@ -74,8 +74,7 @@ module_name()
 {
 	# Do we have "submodule.<something>.path = $1" defined in .gitmodules file?
 	re=$(printf '%s' "$1" | sed -e 's/[].[^$\\*]/\\&/g')
-	name=$( GIT_CONFIG=.gitmodules \
-		git config --get-regexp '^submodule\..*\.path$' |
+	name=$( git config -f .gitmodules --get-regexp '^submodule\..*\.path$' |
 		sed -n -e 's|^submodule\.\(.*\)\.path '"$re"'$|\1|p' )
        test -z "$name" &&
        die "No submodule mapping found in .gitmodules for path '$path'"
@@ -198,8 +197,8 @@ cmd_add()
 	git add "$path" ||
 	die "Failed to add submodule '$path'"
 
-	GIT_CONFIG=.gitmodules git config submodule."$path".path "$path" &&
-	GIT_CONFIG=.gitmodules git config submodule."$path".url "$repo" &&
+	git config -f .gitmodules submodule."$path".path "$path" &&
+	git config -f .gitmodules submodule."$path".url "$repo" &&
 	git add .gitmodules ||
 	die "Failed to register submodule '$path'"
 }
@@ -240,7 +239,7 @@ cmd_init()
 		url=$(git config submodule."$name".url)
 		test -z "$url" || continue
 
-		url=$(GIT_CONFIG=.gitmodules git config submodule."$name".url)
+		url=$(git config -f .gitmodules submodule."$name".url)
 		test -z "$url" &&
 		die "No url found for submodule path '$path' in .gitmodules"