usb: gadget: mass storage: fix return of delayed status

Mass storage gadget returns DELAYED_STATUS in stead of
USB_GADGET_DELAYED_STATUS while handling bulk reset request. Since
peripheral driver uses USB_GADGET_DELAYED_STATUS for delayed status
handling, therefore replace DELAYED_STATUS by USB_GADGET_DELAYED_STATUS
in mass storage driver.

Since, DELAYED_STATUS and hence EP0_BUFSIZE will no longer be used now,
so remove them.

Signed-off-by: Pratyush Anand <pratyush.anand@st.com>
Cc: Paul Zimmerman <Paul.Zimmerman@synopsys.com>
Cc: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Felipe Balbi <balbi@ti.com>