usb: dwc2: gadget: don't modify pullup status during reset

Pullup doesn't need to be enabled during usb reset since it is
already enabled. This leads to shorter chirp-k duration if done
during usb reset.

Tested-by: Robert Baldyga <r.baldyga@samsung.com>
Acked-by: John Youn <johnyoun@synopsys.com>
Signed-off-by: Gregory Herrero <gregory.herrero@intel.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>