iwlwifi: pcie: warn if paging is already initialized during init

iwlwifi: pcie: warn if paging is already initialized during init

This appears to happen in some cases, like when iwlmvm is unloaded and
loaded again without also unloading iwlwifi. Warn in this case and free
the paging data to be able to continue without causing corruption and
kernel crashes due to it (otherwise, paging data is overwritten, but
dram->paging_cnt gets to be twice as big as it should be, and then an
eventual free will crash.)

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>