rt2500usb: truly disable encryption when initialize

Without cipher part nullify of TXRX_CSR0 register we can receive
corrupted frames (removed IV or IVC), after reloading rt2500usb module
with nohwcrypt=1 option, if previous some keys were configured into
the hardware.
Signed-off-by: Stanislaw Gruszka <sgruszka@redhat.com>
Acked-by: Ivo van Doorn <IvDoorn@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

drivers/net/wireless/rt2x00/rt2500usb.c

@@ -817,6 +817,7 @@ static int rt2500usb_init_registers(struct rt2x00_dev *rt2x00dev)
 	rt2500usb_register_write(rt2x00dev, MAC_CSR8, reg);
 
 	rt2500usb_register_read(rt2x00dev, TXRX_CSR0, &reg);
+	rt2x00_set_field16(&reg, TXRX_CSR0_ALGORITHM, CIPHER_NONE);
 	rt2x00_set_field16(&reg, TXRX_CSR0_IV_OFFSET, IEEE80211_HEADER);
 	rt2x00_set_field16(&reg, TXRX_CSR0_KEY_ID, 0);
 	rt2500usb_register_write(rt2x00dev, TXRX_CSR0, reg);