usb: renesas_usbhs: kill dead code in usbhs_probe()

usbhsc_drvcllbck_notify_hotplug() always returns 0, so it's rather pointless to
store and check its result for being < 0.

Signed-off-by: Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>