iwlwifi: fix D3 debug data buffer memory leak

If the driver is unloaded when D3 debug data pulling is enabled
but not triggered, it doesn't release the data buffer.

Fix this by adding iwl_fw_runtime_free and calling it from the
relevant places.

Fixes: 2d8c2615 ("iwlwifi: add d3 debug data support")
Signed-off-by: Shahar S Matityahu <shahar.s.matityahu@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>