sunxi: Fix serial console for A10s-OLinuXino-MICRO

On this board CONFIG_CONS_INDEX needs to be 1 unlike other sun5i
boards.  Since this is the default, remove to bogus setting.

Fixes: 7095f864 ("sunxi: Convert CONS_INDEX to Kconfig")
Signed-off-by: Mark Kettenis <kettenis@openbsd.org>
Reviewed-by: Andre Przywara <andre.przywara@arm.com>
Signed-off-by: Andre Przywara <andre.przywara@arm.com>