usb: gadget: core: unmap request from DMA only if previously mapped

In the SG case this is already handled since a non-zero
request->num_mapped_sgs is a clear indicator that dma_map_sg()
had been called. While it would be nice to do the same for the
singly mapped case by simply checking for non-zero request->dma,
it's conceivable that 0 is a valid dma_addr_t handle. Hence add
a flag 'dma_mapped' to struct usb_request and use this to
determine the need to call dma_unmap_single(). Otherwise, if a
request is not DMA mapped then the result of calling
usb_request_unmap_request() would safely be a no-op.

Signed-off-by: Jack Pham <jackp@codeaurora.org>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>

include/linux/usb/gadget.h

@@ -48,6 +48,7 @@ struct usb_ep;
  *     by adding a zero length packet as needed;
  * @short_not_ok: When reading data, makes short packets be
  *     treated as errors (queue stops advancing till cleanup).
+ * @dma_mapped: Indicates if request has been mapped to DMA (internal)
  * @complete: Function called when request completes, so this request and
  *	its buffer may be re-used.  The function will always be called with
  *	interrupts disabled, and it must not sleep.
@@ -103,6 +104,7 @@ struct usb_request {
 	unsigned		no_interrupt:1;
 	unsigned		zero:1;
 	unsigned		short_not_ok:1;
+	unsigned		dma_mapped:1;
 
 	void			(*complete)(struct usb_ep *ep,
 					struct usb_request *req);