clk: samsung: Silence sparse warnings

drivers/clk/samsung/clk-exynos5260.c:138:40: warning: Using plain integer as NULL pointer
drivers/clk/samsung/clk-exynos5260.c:328:40: warning: Using plain integer as NULL pointer
drivers/clk/samsung/clk-exynos5260.c:392:40: warning: Using plain integer as NULL pointer
drivers/clk/samsung/clk-exynos5260.c:494:40: warning: Using plain integer as NULL pointer
drivers/clk/samsung/clk-exynos5260.c:583:40: warning: Using plain integer as NULL pointer
drivers/clk/samsung/clk-exynos5260.c:644:40: warning: Using plain integer as NULL pointer
drivers/clk/samsung/clk-exynos5260.c:779:40: warning: Using plain integer as NULL pointer
drivers/clk/samsung/clk-exynos5260.c:898:40: warning: Using plain integer as NULL pointer
drivers/clk/samsung/clk-exynos5260.c:962:40: warning: Using plain integer as NULL pointer
drivers/clk/samsung/clk-exynos5260.c:1018:40: warning: Using plain integer as NULL pointer
drivers/clk/samsung/clk-exynos5260.c:1165:40: warning: Using plain integer as NULL pointer
drivers/clk/samsung/clk-exynos5260.c:1373:40: warning: Using plain integer as NULL pointer
drivers/clk/samsung/clk-exynos5260.c:1829:40: warning: Using plain integer as NULL pointer

Acked-by: Sylwester Nawrocki <s.nawrocki@samsung.com>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>