blackfin: Fix warning about undefined function

get_sclk() was not defined in bfin_wdt.c, include the corresponding header.

Cc: Sonic Zhang <sonic.adi@gmail.com>
Signed-off-by: Vasili Galka <vvv444@gmail.com>

drivers/watchdog/bfin_wdt.c

@@ -9,6 +9,7 @@
 #include <common.h>
 #include <watchdog.h>
 #include <asm/blackfin.h>
+#include <asm/clock.h>
 #include <asm/mach-common/bits/watchdog.h>
 
 void hw_watchdog_reset(void)