usb: gadget: udc: renesas_usb3: should call pm_runtime_enable() before add udc

This patch fixes an issue that this driver causes panic if a gadget
driver is already loaded because usb_add_gadget_udc() might call
renesas_usb3_start() via .udc_start, and then pm_runtime_get_sync()
in renesas_usb3_start() doesn't work correctly.
Note that the usb3_to_dev() macro should not be called at this timing
because the macro uses the gadget structure.

Fixes: cf06df3f ("usb: gadget: udc: renesas_usb3: move pm_runtime_{en,dis}able()")
Cc: <stable@vger.kernel.org> # v4.15+
Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Reviewed-by: Simon Horman <horms+renesas@verge.net.au>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>