mwifiex: fix [-Wunused-function] warnings on pcie suspend/resume

drivers/net/wireless/mwifiex/pcie.c:204:12: warning:
  'mwifiex_pcie_resume' defined but not used [-Wunused-function]
drivers/net/wireless/mwifiex/pcie.c:166:12: warning:
  'mwifiex_pcie_suspend' defined but not used [-Wunused-function]

The suspend/resume handlers ought to be under CONFIG_PM directive.

Reported-by: kbuild test robot <fengguang.wu@intel.com>
Signed-off-by: Bing Zhao <bzhao@marvell.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>