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>

(cherry picked from commit aef11279)
Bug: 242344221
Change-Id: I7eddc039ec0c54982fd6bae95af2f73f4ce04ef6
Signed-off-by: Avichal Rakesh <arakesh@google.com>