storage/stream: elimination of usage of the flash API internals

Module was using flash driver implementation API call
`page_layout()` which is part driver implementation
interface API.

This patch re-implement this part of code using
`flash_page_foreach()` public API function.

Signed-off-by: Andrzej Puzdrowski <andrzej.puzdrowski@nordicsemi.no>
1 file changed