iwlwifi: fix access to prph when transport is stopped

When getting HW rfkill we get stop_device being called from
two paths.
One path is the IRQ calling stop device, and updating op
mode and stack.
As a result, cfg80211 is running rfkill sync work that shuts
down all devices (second path).
In the second path, we eventually get to iwl_mvm_stop_device
which calls iwl_fw_dump_conf_clear->iwl_fw_dbg_stop_recording,
that access periphery registers.
The device may be stopped at this point from the first path,
which will result with a failure to access those registers.
Simply checking for the trans status is insufficient, since
the race will still exist, only minimized.
Instead, move the stop from iwl_fw_dump_conf_clear (which is
getting called only from stop path) to the transport stop
device function, where the access is always safe.
This has the added value, of actually stopping dbgc before
stopping device even when the stop is initiated from the
transport.

Fixes: 1efc3843 ("iwlwifi: stop dbgc recording before stopping DMA")
Signed-off-by: Sara Sharon <sara.sharon@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>