iwlwifi: pcie: fix locking when "HW not ready"

If we run into this error path, we shouldn't unlock the mutex
since it's not locked since. Fix this.

Fixes: a6bd005f

 ("iwlwifi: pcie: fix RF-Kill vs. firmware load race")
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/iwlwifi.20220128142706.5d16821d1433.Id259699ddf9806459856d6aefbdbe54477aecffd@changeid