usb: dwc3: gadget: increment request->actual once

commit c7de573471832dff7d31f0c13b0f143d6f017799 upstream.

When using SG lists, we would end up setting
request->actual to:

	num_mapped_sgs * (request->length - count)

Let's fix that up by incrementing request->actual
only once.

Reported-by: Brian E Rogers <brian.e.rogers@intel.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>
Signed-off-by: Willy Tarreau <w@1wt.eu>
[@nathanchance: fixed conflicts related to e8244d86]
Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>