Exynos: pwm: Use generic api to get pwm clk freq

Use generic api to get the pwm clock frequency

Test with command "sf probe 1:0; time sf read 40008000 0 1000".
Try with different numbers of bytes and see that sane values are obtained
Build and boot U-boot with this patch, backlight works properly.

Signed-off-by: Padmavathi Venna <padma.v@samsung.com>
Signed-off-by: Akshay Saraswat <akshay.s@samsung.com>
Acked-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Minkyu Kang <mk7.kang@samsung.com>

arch/arm/cpu/armv7/exynos/clock.c

@@ -1354,7 +1354,7 @@ unsigned long get_i2c_clk(void)
 unsigned long get_pwm_clk(void)
 {
 	if (cpu_is_exynos5())
-		return exynos5_get_pwm_clk();
+		return clock_get_periph_rate(PERIPH_ID_PWM0);
 	else {
 		if (proid_is_exynos4412())
 			return exynos4x12_get_pwm_clk();