rsi: remove redundant duplicate assignment of buffer_size

Variable buffer_size is re-assigned the same value, this duplicated
assignment is redundant and can be removed.

Cleans up clang warning:
drivers/net/wireless/rsi/rsi_91x_usb.c:140:4: warning: Value stored
to 'buffer_size' is never read
Signed-off-by: NColin Ian King <colin.king@canonical.com>
Signed-off-by: NKalle Valo <kvalo@codeaurora.org>

drivers/net/wireless/rsi/rsi_91x_usb.c

@@ -140,7 +140,6 @@ static int rsi_find_bulk_in_and_out_endpoints(struct usb_interface *interface,
 			buffer_size = endpoint->wMaxPacketSize;
 			dev->bulkout_endpoint_addr[bout_found] =
 				endpoint->bEndpointAddress;
-			buffer_size = endpoint->wMaxPacketSize;
 			dev->bulkout_size[bout_found] = buffer_size;
 			bout_found++;
 		}