iwlwifi: mvm: make init_dbg effective only on failure

If FW loads without a problem, leaving init_dbg on can
cause a confusion, since the user won't necessarily
remember it is still turned on, and there are flows in
which everything continues as usual, only without
stopping the device after INIT, even if there is no FW
assert. On 22000 HW, for instance, this causes a
warning, since the paging is getting initialized twice.

Solve the issue by making this module param effective
only if the FW indeed asserts during INIT.

Signed-off-by: Liad Kaufman <liad.kaufman@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>