storage/stream_flash: Fix range check in stream_flash_erase_page

Added check where stream_flash_erase_page checks if requested
offset is actually within stream flash designated area.

Fixes #79800

Signed-off-by: Dominik Ermel <dominik.ermel@nordicsemi.no>
(cherry picked from commit 8714c172edd1947a6348ac0f669d89668f5896c3)
2 files changed