arm: spear13xx: Fix spics gpio controller's warning

This fixes the following warning by also sending the flags argument for
gpio controllers:

Property 'cs-gpios', cell 6 is not a phandle reference in
/ahb/apb/spi@e0100000

Fixes: 8113ba91 ("ARM: SPEAr: DT: Update device nodes")
Cc: stable@vger.kernel.org # v3.8+
Reported-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Olof Johansson <olof@lixom.net>