wifi: iwlwifi: dbg-tlv: clear FW debug memory on init

wifi: iwlwifi: dbg-tlv: clear FW debug memory on init

When we restart the firmware, we shouldn't keep old debug data
around. Since the "allocate" function might not reallocate the
memory blocks (they're only freed when we unbind from the device),
clear the memory to have a clean slate for debug data.

This is a bit more complex since we normally don't enter into
the allocation function, but duplicating the logic didn't seem
enticing either, so rework the allocation a bit to always go
into the individual block allocation, but there clear if it's
already allocated, rather than allocating again.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Gregory Greenman <gregory.greenman@intel.com>
Link: https://lore.kernel.org/r/20230613155501.30b82881cfbf.I39520aff8ac95ee64d39dc5913525a1efd7995fa@changeid
Signed-off-by: Johannes Berg <johannes.berg@intel.com>