ARM: imx: Kconfig: Fix typo in help

Fix typo from i.MX31 to i.MX35 in i.MX35's help.

Signed-off-by: Nobuhiro Iwamatsu <nobuhiro1.iwamatsu@toshiba.co.jp>
Reviewed-by: Fabio Estevam <festevam@gmail.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>