rt2800usb: initialize H2M_INT_SRC register

Ralink USB driver initialize H2M_INT_SRC to 0 after firmware load, and
never touch this register later. It is not touched at all by Ralink PCI
driver.
Acked-by: NHelmut Schaa <helmut.schaa@googlemail.com>
Acked-by: NIvo van Doorn <IvDoorn@gmail.com>
Signed-off-by: NStanislaw Gruszka <sgruszka@redhat.com>
Signed-off-by: NJohn W. Linville <linville@tuxdriver.com>

drivers/net/wireless/rt2x00/rt2800lib.c

@@ -448,6 +448,8 @@ int rt2800_load_firmware(struct rt2x00_dev *rt2x00dev,
 	 */
 	rt2800_register_write(rt2x00dev, H2M_BBP_AGENT, 0);
 	rt2800_register_write(rt2x00dev, H2M_MAILBOX_CSR, 0);
+	if (rt2x00_is_usb(rt2x00dev))
+		rt2800_register_write(rt2x00dev, H2M_INT_SRC, 0);
 	msleep(1);
 
 	return 0;