iwlwifi: fix apm_stop (wrong bit polarity for FLAG_INIT_DONE)

The patch fixes CSR_GP_CNTRL_REG_FLAG_INIT_DONE was set instead of
cleared which disabled moving device to D0U state.

Signed-off-by: Mohamed Abbas <mohamed.abbas@intel.com>
Signed-off-by: Tomas Winkler <tomas.winkler@intel.com>
Signed-off-by: Zhu Yi <yi.zhu@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>