iwlwifi: check return value of pci_enable_device

pci_enable_device is tagged with __must_check therefore
don't ignore the return value in pci_resume handlers

Signed-off-by: Tomas Winkler <tomas.winkler@intel.com>
Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>