usb: dwc2: gadget: move setting last reset time to s3c_hsotg_core_init

This patch removes duplicated code and sets last_rst variable in the
function which does the hardware reset.

Acked-by: Paul Zimmerman <paulz@synopsys.com>
Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>