usb/net/r815x: fix cast to restricted __le32

>> drivers/net/usb/r815x.c:38:16: sparse: cast to restricted __le32
>> drivers/net/usb/r815x.c:67:15: sparse: cast to restricted __le32
>> drivers/net/usb/r815x.c:69:13: sparse: incorrect type in assignment (different base types)
   drivers/net/usb/r815x.c:69:13:    expected unsigned int [unsigned] [addressable] [assigned] [usertype] tmp
   drivers/net/usb/r815x.c:69:13:    got restricted __le32 [usertype] <noident>

Signed-off-by: Hayes Wang <hayeswang@realtek.com>
Spotted-by: kbuild test robot <fengguang.wu@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>