iwlwifi: pcie: clear RFKILL interrupt in AMPG

If we forget to do so, we can't send HCMD to firmware while
the NIC is in RFKILL state.

Cc: stable@vger.kernel.org
Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>