iwlwifi: pcie: free context info in case of failures

If iwl_pcie_ctxt_info_init_fw_sec() fails, the previous allocated DMA
memory needs to be freed (it even goes out of scope immediately.)
Do that to prevent the leak.

Fixes: eda50cde

 ("iwlwifi: pcie: add context information support")
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>