r8152: remove sram_read

Read OCP register 0xa43a~0xa43b would clear some flags which the hw
would use, and it may let the device lost. However, the unit of
reading is 4 bytes. That is, it would read 0xa438~0xa43b when calling
sram_read() to read OCP_SRAM_DATA.

Signed-off-by: Hayes Wang <hayeswang@realtek.com>
Signed-off-by: David S. Miller <davem@davemloft.net>