kconfig: Fix choice symbol expression leak

When propagating dependencies from parents after parsing, an expression
node is allocated if the parent symbol is a 'choice'. This node was
never freed.

Outline of leak:

	if (sym && sym_is_choice(sym)) {
		...
		*Allocate (in this case only)*
		parentdep = expr_alloc_symbol(sym);
	} else if (parent->prompt)
		parentdep = parent->prompt->visible.expr;
	else
		parentdep = parent->dep;

	for (menu = parent->list; menu; menu = menu->next) {
		...
		*Copy*
		basedep = expr_alloc_and(expr_copy(parentdep), basedep);
		...
	}
	*parentdep lost if the parent is a choice!*

Fix by freeing 'parentdep' after the loop if the parent symbol is a
choice. Note that this only frees the expression node and not the choice
symbol itself.

Summary from Valgrind on 'menuconfig' (ARCH=x86) before the fix:

	LEAK SUMMARY:
	   definitely lost: 1,608 bytes in 67 blocks
	   ...

Summary after the fix:

	LEAK SUMMARY:
	   definitely lost: 0 bytes in 0 blocks
	   ...

Signed-off-by: Ulf Magnusson <ulfalizer@gmail.com>
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>

1 files changed, 3 insertions, 0 deletions

diff --git a/scripts/kconfig/menu.c b/scripts/kconfig/menu.c
index 5b2415991c3e..41c79bef3d07 100644
--- a/scripts/kconfig/menu.c
+++ b/scripts/kconfig/menu.c
@@ -408,6 +408,9 @@ void menu_finalize(struct menu *parent)
 			}
 		}
 
+		if (sym && sym_is_choice(sym))
+			expr_free(parentdep);
+
 		/*
 		 * Recursively process children in the same fashion before
 		 * moving on