fix build error for bf527-ezkit_defconfig for old silicon

Signed-off-by: Aaron Wu <Aaron.wu@analog.com>

fix build error for bf527-ezkit_defconfig for old silicon

arch/blackfin/configs/BF527-EZKIT_defconfig

@@ -146,6 +146,7 @@ CONFIG_USB_DEVICEFS=y
 CONFIG_USB_OTG_BLACKLIST_HUB=y
 CONFIG_USB_MON=y
 CONFIG_USB_MUSB_HDRC=y
+CONFIG_MUSB_PIO_ONLY=y
 CONFIG_USB_MUSB_BLACKFIN=y
 CONFIG_MUSB_PIO_ONLY=y
 CONFIG_USB_STORAGE=y