i2c: Remove 'default n' from busses/Kconfig

The default value for a config option defaults to 'n' so it doesn't need
to be set here.

Signed-off-by: Jarkko Nikula <jarkko.nikula@linux.intel.com>
Reviewed-by: Jean Delvare <jdelvare@suse.de>
[jdelvare: found another one]
Signed-off-by: Wolfram Sang <wsa@kernel.org>