usb: gadget: uvc: drop unnecessary check for always set req

usb: gadget: uvc: drop unnecessary check for always set req

The pump function is running in an while(1) loop. The only case this
loop will be escaped is the two breaks. In both cases the req is valid.
Therefor the check for an not set req can be dropped and setting the req
to NULL does also has never any effect.

Signed-off-by: Michael Grzeschik <m.grzeschik@pengutronix.de>
Link: https://lore.kernel.org/r/20240214-uvc-gadget-cleanup-v1-1-de6d78780459@pengutronix.de
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>