usb: gadget: uvc: improve sg exit condition

commit aef11279 upstream.

The exit condition to quit iterating over the sg_list, while encoding
the sg entries, has to consider the case that the dma_len of the entry
could be zero. This patch takes this condition to account.

Signed-off-by: Michael Grzeschik <m.grzeschik@pengutronix.de>
Link: https://lore.kernel.org/r/20220402232744.3622565-4-m.grzeschik@pengutronix.de


Cc: Dan Vacura <w36195@motorola.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>