ARM: 9212/1: domain: Modify Kconfig help text

After the removal of set_fs() the reference to set_fs() is stale.
Alter the helptext to reflect what the config option really does.

Fixes: 8ac6f5d7 ("ARM: 9113/1: uaccess: remove set_fs() implementation")
Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>