doc: nvmem: Update example

Update the example to reflect the new API. I have chosen the brcm-nvram
driver since it seems to be simpler than the qfprom driver.

Signed-off-by: Sean Anderson <sean.anderson@seco.com>
Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Link: https://lore.kernel.org/r/20220220151527.17216-12-srinivas.kandagatla@linaro.org


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>