iwlwifi: fix __devexit_p points to __devexit functions

The iwlxxxx_pci_remove functions are not needed when drivers are not
compiled as modules - they can thus be discarded at kernel link time.
This is already captured by having them as __devexit_p in the pci_driver
struct - these are supposed to be pointers to __devexit functions, but was not.
This is now fixed.

This problem was reported by Toralf Forster when testing the compilation of
2.6.25-rc6.

Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>
CC: Toralf Forster <toralf.foerster@gmx.de>
Signed-off-by: Tomas Winkler <tomas.winkler@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>