iwlwifi: avoid void pointer arithmetic

iwlwifi: avoid void pointer arithmetic

[ Upstream commit 3827cb59b3b8ce4b1687385d35034dadcd90d7ce ]

Avoid void pointer arithmetic since it's technically
undefined and causes warnings in some places that use
our code.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>
Link: https://lore.kernel.org/r/iwlwifi.20220128153014.e349104ecd94.Iadc937f475158b9437becdfefb361a97e7eaa934@changeid
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>
Stable-dep-of: 8ba438ef3cac ("wifi: iwlwifi: mvm: Fix a memory corruption issue")
Signed-off-by: Sasha Levin <sashal@kernel.org>