iwlwifi: pnvm: read EFI data only if long enough

If the data we get from EFI is not even long enough for
the package struct we expect then ignore it entirely.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Fixes: a1a6a4cf ("iwlwifi: pnvm: implement reading PNVM from UEFI")
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/iwlwifi.20211016114029.33feba783518.I54a5cf33975d0330792b3d208b225d479e168f32@changeid