commit 23fd537c upstream.

Always unmap all SG entries as required by DMA API

Fixes: a698908d ("usb: gadget: add generic map/unmap request utilities")
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>
[bwh: Backported to 3.16: adjust filename, context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>