storeage/stream_flash: Cache write_block_size to ctx on init

The commit caches write_block_size and erase_value to stream flash
context, at init, to avoid calling Flash API multiple times
to get these values at various stages of code exectuion,
at run-time.

Signed-off-by: Dominik Ermel <dominik.ermel@nordicsemi.no>
2 files changed