[ARM] 2852/1: Correct the mistake in arch/arm/mm/Kconfig file

Patch from Sean Lee

In the arch/arm/mm/Kconfig file, the CPU_DCACHE_WRITETHROUGH
option is depend on the CPU_DISABLE_DCACHE, but the "Disable
D-Cache" option is configured as CPU_DCACHE_DISABLE.
The CPU_DISABLE_DCACHE should be CPU_DCACHE_DISABLE

Signed-off-by: Sean Lee <beginner2arm@eyou.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>