blackfin: Add <asm/clock.h> to numerous drivers

With d6a320d we moved some clock externs out of blackfin_local.h and
into clock.h but now need to include <asm/clock.h> in more drivers to
avoid warnings.

Cc: Sonic Zhang <sonic.zhang@analog.com>
Signed-off-by: Tom Rini <trini@ti.com>
diff --git a/drivers/usb/musb/blackfin_usb.c b/drivers/usb/musb/blackfin_usb.c
index 35268ba..65fff88 100644
--- a/drivers/usb/musb/blackfin_usb.c
+++ b/drivers/usb/musb/blackfin_usb.c
@@ -11,6 +11,7 @@
 #include <usb.h>
 
 #include <asm/blackfin.h>
+#include <asm/clock.h>
 #include <asm/mach-common/bits/usb.h>
 
 #include "musb_core.h"