UPSTREAM: usb: gadget: uvc: improve sg exit condition

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


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Bug: 249635012
(cherry picked from commit aef11279)
Change-Id: I5e7b7c53652d564c0a6424d3d4b7797e64270315
Signed-off-by: Dan Vacura <w36195@motorola.com>