nvmem: imx-ocotp: Fix assignment warning.

This patch fixes below error if the driver is compiled with 64 bit
machine configuration.

"drivers/nvmem/imx-ocotp.c:102:14: warning: assignment makes integer
from pointer without a cast"

Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Acked-by: Philipp Zabel <p.zabel@pengutronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>