iwlagn: fix compile warnings when CONFIG_PM_SLEEP is not set

  CC [M]  drivers/net/wireless/iwlwifi/iwl-pci.o
  drivers/net/wireless/iwlwifi/iwl-pci.c:506: warning: ‘iwl_pci_suspend’ defined but not used
  drivers/net/wireless/iwlwifi/iwl-pci.c:519: warning: ‘iwl_pci_resume’ defined but not used

These are only used if CONFIG_PM_SLEEP is enabled. CONFIG_PM depends
(CONFIG_PM_SLEEP || CONFIG_PM_RUNTIME), so it can be set without
CONFIG_PM_SLEEP selected.

Signed-off-by: Daniel Halperin <dhalperi@cs.washington.edu>
Signed-off-by: Wey-Yi Guy <wey-yi.w.guy@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>