i2c: sandbox: remove code snippet from Kconfig help

i2c: sandbox: remove code snippet from Kconfig help

With the Kconfig re-sync with Linux 4.10, characters such as
'}', ';' in Kconfig help message cause warnings:

$ make defconfig
*** Default configuration is based on 'sandbox_defconfig'
drivers/i2c/Kconfig:132:warning: ignoring unsupported character '}'
drivers/i2c/Kconfig:132:warning: ignoring unsupported character ';'

Drop the Device Tree fragment from the help.

Acked-by: Heiko Schocher <hs@denx.de>
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>