[media] dib0700: Drop useless check when remote key is pressed
struct dvb_usb_device *d can never be NULL so don't waste time
checking for this.
Rationale: the urb's context is set when usb_fill_bulk_urb() is called
in dib0700_rc_setup(), and never changes after that. d is dereferenced
unconditionally in dib0700_rc_setup() so it can't be NULL or the
driver would crash right away.