staging: rtl8712: re-use native mac_pton() helper

There is a nice helper to parse MAC. Let's use it and remove custom
implementation.
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/rtl8712/usb_intf.c

@@ -353,11 +353,6 @@ static void disable_ht_for_spec_devid(const struct usb_device_id *pdid,
 	}
 }
 
-static u8 key_2char2num(u8 hch, u8 lch)
-{
-	return (hex_to_bin(hch) << 4) | hex_to_bin(lch);
-}
-
 /*
  * drv_init() - a device potentially for us
  *
@@ -465,16 +460,7 @@ static int r871xu_drv_init(struct usb_interface *pusb_intf,
 				r8712_efuse_pg_packet_read(padapter, offset,
 						     &pdata[i]);
 
-			if (r8712_initmac) {
-				/* Users specify the mac address */
-				int jj, kk;
-
-				for (jj = 0, kk = 0; jj < ETH_ALEN;
-				     jj++, kk += 3)
-					mac[jj] =
-					   key_2char2num(r8712_initmac[kk],
-					   r8712_initmac[kk + 1]);
-			} else {
+			if (!r8712_initmac || !mac_pton(r8712_initmac, mac)) {
 				/* Use the mac address stored in the Efuse
 				 * offset = 0x12 for usb in efuse
 				 */