staging: dwc2: remove dummy interrupt handling

The handling for the IC2INT and RESTOREDONE interrupts just cleared the
interrupt flag, but did not do anything else. Since these interrupts are
not enabled anywhere, they should never trigger and there should never
be a need to clear their flags, so we can safely remove this code.

Signed-off-by: Matthijs Kooijman <matthijs@stdin.nl>
Acked-by: Paul Zimmerman <paulz@synopsys.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>