nvmem: sc27xx: Convert nvmem offset to block index

The Spreadtrum SC27XX efuse data are organized by blocks and each block
contains 2 bytes data. Moreover the nvmem core always pass the offset
in byte to the controller, so we should change the offset in byte to
the correct block index and block offset to read the data.

Signed-off-by: Freeman Liu <freeman.liu@unisoc.com>
Signed-off-by: Baolin Wang <baolin.wang@linaro.org>
Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>