r8152: fix writing USB_BP2_EN

The register of USB_BP2_EN is 16 bits, so we should use
ocp_write_word(), not ocp_write_byte().

Fixes: 9370f2d0 ("support request_firmware for RTL8153")
Signed-off-by: Hayes Wang <hayeswang@realtek.com>
Signed-off-by: David S. Miller <davem@davemloft.net>