Exynos: clock: Correct pwm source clk selection

MPLL is selected as the source clk of pwm by default

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: NPadmavathi Venna <padma.v@samsung.com>
Signed-off-by: NAkshay Saraswat <akshay.s@samsung.com>
Acked-by: NSimon Glass <sjg@chromium.org>
Signed-off-by: NMinkyu Kang <mk7.kang@samsung.com>

board/samsung/smdk5250/setup.h

@@ -343,7 +343,7 @@
 #define TOP2_VAL		0x0110000
 
 /* CLK_SRC_PERIC0 */
-#define PWM_SEL		0
+#define PWM_SEL		6
 #define UART3_SEL	6
 #define UART2_SEL	6
 #define UART1_SEL	6