git.sh: simplify prep_submodules()

copying the module list into tmpdir/ no longer makes sense,
because it was only done before when we supported either
running the list from "git submodule update", or module.list.

since we only support handling of module.list, we can
greatly simplify this function.

Signed-off-by: Leah Rowe <leah@libreboot.org>

include/git.sh

@@ -106,13 +106,9 @@ prep_submodules()
 	mdir="$PWD/config/submodule/$project"
 	[ -n "$tree" ] && mdir="$mdir/$tree"
 
-	[ -f "$mdir/module.list" ] || return 0
-	cat "$mdir/module.list" > "$tmpdir/modules" || \
-	    $err "!cp $mdir/module.list $tmpdir/modules"
-
-	while read -r msrcdir; do
+	[ -f "$mdir/module.list" ] && while read -r msrcdir; do
 		fetch_submodule "$msrcdir"
-	done < "$tmpdir/modules"
+	done < "$mdir/module.list"; return 0
 }
 
 fetch_submodule()
@@ -128,6 +124,7 @@ fetch_submodule()
 	done
 
 	rm -Rf "$tmpgit/$1" || $err "!rm '$mdir' '$1'"
+
 	tmpclone "$subrepo" "$subrepo_bkup" "$tmpdir/$1" "$subrev" \
 	    "$mdir/${1##*/}/patches"
 }