dt-bindings: clock: samsung: fix header path in example

The proper header is exynos4.h:

    samsung,exynos4412-isp-clock.example.dts:19:18: fatal error: dt-bindings/clock/exynos4412.h: No such file or directory

Fixes: 7ac615780926 ("dt-bindings: clock: samsung: convert Exynos4 to dtschema")
Reported-by: Stephen Boyd <sboyd@kernel.org>
Reported-by: Rob Herring <robh+dt@kernel.org>
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
Link: https://lore.kernel.org/r/20210831130643.83249-1-krzysztof.kozlowski@canonical.com
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Stephen Boyd <sboyd@kernel.org>