iwlagn: merge iwl_pci_down and iwl_pci_remove

The latter was the only place that called the first. The two
functions were split when the iwl_pci_probe called iwl_pci_down
upon failure in the probe. Since iwl_pci_probe undoes its work by
itself, there is no need to split between iwl_pci_down, and
iwl_pci_remove.

Thanks to Pavel Roskin for pointing that out.

Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>
Signed-off-by: Wey-Yi Guy <wey-yi.w.guy@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>