iwlwifi: fix various more -Wcast-qual warnings

When enabling W=3 that gets us -Wcast-qual, fix those warnings
in the code and propagate constness properly, or cast it away
via (uintptr_t) where really needed.

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.20220128153014.4ac2f19c121e.Ied9469d93f8199206242bfba96e4e8d1949e3a08@changeid
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>