usb: dwc3: gadget: don't request IRQs in atomic

We cannot request an IRQ with spinlocks held
as that would trigger a sleeping inside
spinlock warning.

Cc: <stable@vger.kernel.org> # v3.10
Reported-by: Stephen Boyd <sboyd@codeaurora.org>
Signed-off-by: Felipe Balbi <balbi@ti.com>