iwlwifi: pcie: fix SW error MSI-X mapping

We need to also update the IVAR location, since we've shifted
the bit.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Fixes: 571836a0

 ("iwlwifi: pcie: update sw error interrupt for BZ family")
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>
Link: https://lore.kernel.org/r/iwlwifi.20220304131517.bcfb28484e50.I921df6b5134785d7eeb0c934e4a43157c582fa79@changeid
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>