dt-bindings: phy: samsung,ufs-phy: match clock items

Below error is detected from dtbs_check. exynos7-ufs-phy is required
symbol clocks otherwise only PLL ref clock is required.

clock-names: ['ref_clk'] is too short

Reported-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Suggested-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Suggested-by: Alim Akhtar <alim.akhtar@samsung.com>
Signed-off-by: Chanho Park <chanho61.park@samsung.com>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20220725000249.30509-1-chanho61.park@samsung.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>