An unsigned long variable should rely on '%lu' format strings, not '%zd'

Fixes: a1a6a4cf ("iwlwifi: pnvm: implement reading PNVM from UEFI")
Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Acked-by: Luca Coelho <luciano.coelho@intel.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20210302011640.1276636-1-pierre-louis.bossart@linux.intel.com