r8152: Remove unused function usb_ocp_read()

The function is not used, removing it fixes the following warning when
building with clang:

drivers/net/usb/r8152.c:825:5: error: unused function 'usb_ocp_read'
    [-Werror,-Wunused-function]
Signed-off-by: NMatthias Kaehlcke <mka@chromium.org>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/usb/r8152.c

@@ -840,12 +840,6 @@ int pla_ocp_write(struct r8152 *tp, u16 index, u16 byteen, u16 size, void *data)
 	return generic_ocp_write(tp, index, byteen, size, data, MCU_TYPE_PLA);
 }
 
-static inline
-int usb_ocp_read(struct r8152 *tp, u16 index, u16 size, void *data)
-{
-	return generic_ocp_read(tp, index, size, data, MCU_TYPE_USB);
-}
-
 static inline
 int usb_ocp_write(struct r8152 *tp, u16 index, u16 byteen, u16 size, void *data)
 {