nvs_flash: replace strncpy + manual null termination with strlcpy
nvs_flash: replace strncpy + manual null termination with strlcpy

Since libbsd is now a build dependency on Linux, strncpy can be
replaced with the safer and less verbose strlcpy.

espressif/esp-idf,espressif/esp-idf,espressif/esp-idf,espressif/esp-idf