ARM: at91: don't provide dt init code for at91x40

at91x40 has no support for device tree, but Kconfig allows
us to enable CONFIG_OF anyway, causing a link error in the
at91 reset controller initialization.

The easiest fix is to adapt the existing #ifdef to omit
the broken code on at91x40 where it is never called anyway.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Nicolas Ferre <nicolas.ferre@atmel.com>
Cc: Andrew Victor <linux@maxim.org.za>
Cc: Jean-Christophe Plagniol-Villard <plagnioj@jcrosoft.com>