usb: dwc2: host: allocate qtd before atomic enqueue

To avoid sleep while atomic bugs, allocate qtd before calling
dwc2_hcd_urb_enqueue. No need to pass mem_flags to
dwc2_hcd_urb_enqueue any more as no memory allocations are done in it.

Acked-by: John Youn <johnyoun@synopsys.com>
Tested-by: Heiko Stuebner <heiko@sntech.de>
Tested-by: Doug Anderson <dianders@chromium.org>
Signed-off-by: Mian Yousaf Kaukab <yousaf.kaukab@intel.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>