usb: dwc3: Don't check usb isochronous endpoint check for ep0

Commit 5ad02fb8 ("usb: dwc3: gadget: move isoc endpoint check
to unlocked set_halt") moved usb isochronous endpoint check form
dwc3_gadget_ep_set_halt() to __dwc3_gadget_ep_set_halt().
dwc3_gadget_ep_set_halt() API is being called explicitly by USB
function driver to stalls USB endpoints whereas
__dwc3_gadget_ep_set_halt() API is also being called to stall ep0
on receiving invalid setup packet or not able to queue response
to setup packet. It is not supposed to have any descriptors with
ep0 early stage of enumeration process. Hence revert change which
makes sure to check usb endpoint type against isochronous before
halting endpoint with dwc3_gadget_ep_set_halt() instead of
__dwc3_gadget_ep_set_halt().

Change-Id: I24b3e78613bf89340c812e353dafaf384ac4a057
Signed-off-by: Mayank Rana <mrana@codeaurora.org>