ARM: dts: tango: Align L2 cache-controller nodename with dtschema

Fix dtschema validator warnings like:
    l2-cache-controller@20100000: $nodename:0:
        'l2-cache-controller@20100000' does not match '^(cache-controller|cpu)(@[0-9a-f,]+)*$'

Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
Acked-by: Mans Rullgard <mans@mansr.com>