samples: Use immediate logging mode in nvs sample

Applying same fix as for watchdog relmated samples
in https://github.com/zephyrproject-rtos/zephyr/pull/52949/


Switching to the immediate logging mode, not by just disabling the
LOG_PRINTK option.Do not direct printk to logging subsystem in the sample.

Signed-off-by: Francois Ramu <francois.ramu@st.com>