iwlwifi: allow pci_enable_msi fail

Continue the init process even fail to enable msi

out_iounmap is no longer used, remove it

Reported-by: werner <w.landgraf@ru.ru>
Tested-by: werner <w.landgraf@ru.ru>
Signed-off-by: Wey-Yi Guy <wey-yi.w.guy@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>