iwlwifi: pcie: propagate iwl_pcie_apm_init's status

iwl_pcie_apm_init can fail so make sure that the caller
takes the status into account.
Also, ensure that the error that iwl_pcie_apm_init can emit
will appear in the kernel log by default.

Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>