blackfin: update defconfig for bf527-ezkit

To fix compile error:
drivers/usb/musb/blackfin.h:51:3: error: #error "Please use PIO mode in MUSB
driver on bf52x chip v0.0 and v0.1"
make[4]: *** [drivers/usb/musb/blackfin.o] Error 1
Signed-off-by: Bob Liu <lliubbo@gmail.com>

arch/blackfin/configs/BF527-EZKIT_defconfig

@@ -147,6 +147,7 @@ CONFIG_USB_OTG_BLACKLIST_HUB=y
 CONFIG_USB_MON=y
 CONFIG_USB_MUSB_HDRC=y
 CONFIG_USB_MUSB_BLACKFIN=y
+CONFIG_MUSB_PIO_ONLY=y
 CONFIG_USB_STORAGE=y
 CONFIG_USB_GADGET=y
 CONFIG_RTC_CLASS=y