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: NSam Ravnborg <sam@ravnborg.org>
Signed-off-by: NMichal Marek <mmarek@suse.cz>