USB: ethernet gadget avoids zlps for musb_hdrc

For systems using the Mentor HDRC controllers we get better TX DMA throughput
if we can avoid falling back to PIO to write zero length packets ... so tell
the driver to avoid ZLPs.

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/usb/gadget/ether.c

@@ -2230,6 +2230,9 @@ eth_bind (struct usb_gadget *gadget)
 	if (gadget_is_pxa (gadget)) {
 		/* pxa doesn't support altsettings */
 		cdc = 0;
+	} else if (gadget_is_musbhdrc(gadget)) {
+		/* reduce tx dma overhead by avoiding special cases */
+		zlp = 0;
 	} else if (gadget_is_sh(gadget)) {
 		/* sh doesn't support multiple interfaces or configs */
 		cdc = 0;