ARM: dts: exynos: Fix regulator name to avoid forbidden character on exynos4210-trats

The usage of slash character causes failure when creating regulator
debugfs entry.

Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
[k.kozlowski: Write commit message]
Signed-off-by: Krzysztof Kozlowski <k.kozlowski@samsung.com>