kconfig: Fix automatic menu creation mem leak

kconfig: Fix automatic menu creation mem leak

expr_trans_compare() always allocates and returns a new expression,
giving the following leak outline:

	...
	*Allocate*
	basedep = expr_trans_compare(basedep, E_UNEQUAL, &symbol_no);
	...
	for (menu = parent->next; menu; menu = menu->next) {
		...
		*Copy*
		dep2 = expr_copy(basedep);
		...
		*Free copy*
		expr_free(dep2);
	}
	*basedep lost!*

Fix by freeing 'basedep' after the loop.

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

	LEAK SUMMARY:
	   definitely lost: 344,376 bytes in 14,349 blocks
	   ...

Summary after the fix:

	LEAK SUMMARY:
	   definitely lost: 44,448 bytes in 1,852 blocks
	   ...

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