btrfs: add assertions where number of devices could go below 0

In preparation to add helper function to deduce the num_devices with
replace running, use assert instead of BUG_ON or WARN_ON. The number of
devices would not normally drop to 0 due to other checks so the assert
is sufficient.

Signed-off-by: Anand Jain <[email protected]>
Reviewed-by: David Sterba <[email protected]>
[ update changelog, adjust the assert condition ]
Signed-off-by: David Sterba <[email protected]>

0 files changed, 0 insertions, 0 deletions