rtlwifi: fix incorrect use of usb_alloc_coherent with usb_control_msg

Incorrect use of usb_alloc_coherent memory as input buffer to usb_control_msg
can cause problems in arch DMA code, for example kernel BUG at
'arch/arm/include/asm/dma-mapping.h:321' on ARM (linux-3.4).

Change _usb_writeN_sync use kmalloc'd buffer instead.

Cc: stable@vger.kernel.org
Signed-off-by: Jussi Kivilinna <jussi.kivilinna@mbnet.fi>
Acked-by: Larry Finger <Larry.Finger@lwfinger.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

drivers/net/wireless/rtlwifi/usb.c

@@ -210,17 +210,16 @@ static void _usb_writeN_sync(struct rtl_priv *rtlpriv, u32 addr, void *data,
 	u16 index = REALTEK_USB_VENQT_CMD_IDX;
 	int pipe = usb_sndctrlpipe(udev, 0); /* write_out */
 	u8 *buffer;
-	dma_addr_t dma_addr;
 
-	wvalue = (u16)(addr&0x0000ffff);
-	buffer = usb_alloc_coherent(udev, (size_t)len, GFP_ATOMIC, &dma_addr);
+	wvalue = (u16)(addr & 0x0000ffff);
+	buffer = kmalloc(len, GFP_ATOMIC);
 	if (!buffer)
 		return;
 	memcpy(buffer, data, len);
 	usb_control_msg(udev, pipe, request, reqtype, wvalue,
 			index, buffer, len, 50);
 
-	usb_free_coherent(udev, (size_t)len, buffer, dma_addr);
+	kfree(buffer);
 }
 
 static void _rtl_usb_io_handler_init(struct device *dev,