usb: gadget: fsl: Fix unsigned expression compared with zero in fsl_udc_probe

udc_controller->irq is "unsigned int" always >= 0, but platform_get_irq may
return little than zero. So "dc_controller->irq < 0" condition is never
accessible.

Acked-by: Li Yang <leoyang.li@nxp.com>
Signed-off-by: Ye Bin <yebin10@huawei.com>
Signed-off-by: Felipe Balbi <balbi@kernel.org>