kconfig: fix savedefconfig for tristate choices

savedefconfig failed to save choice symbols equal to 'y'
for tristate choices.
This resulted in this value being lost.

In particular is fixes an issue where

	make ARCH=avr32 atngw100_defconfig
	make ARCH=avr32 savedefconfig
	cp defconfig arch/avr32/configs/atngw100_defconfig
	make ARCH=avr32 atngw100_defconfig
	diff -u .config .config.old

failed to produce an identical .config.
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Signed-off-by: Michal Marek <mmarek@suse.cz>

scripts/kconfig/confdata.c

@@ -497,7 +497,7 @@ int conf_write_defconfig(const char *filename)
 			/*
 			 * If symbol is a choice value and equals to the
 			 * default for a choice - skip.
-			 * But only if value equal to "y".
+			 * But only if value is bool and equal to "y" .
 			 */
 			if (sym_is_choice_value(sym)) {
 				struct symbol *cs;
@@ -506,8 +506,7 @@ int conf_write_defconfig(const char *filename)
 				cs = prop_get_symbol(sym_get_choice_prop(sym));
 				ds = sym_choice_default(cs);
 				if (sym == ds) {
-					if ((sym->type == S_BOOLEAN ||
-					sym->type == S_TRISTATE) &&
+					if ((sym->type == S_BOOLEAN) &&
 					    sym_get_tristate_value(sym) == yes)
 						goto next_menu;
 				}