iwlwifi: check the SCD conf from ALIVE response

The ALIVE response of new fw inclues the base address of
the SCD in SRAM. Until we read it from a prph register,
which was set by the fw. Since the fw might well stop
updating the prph register, add a WARN when there is an
inconsitency between the ALIVE response and the register
to catch any change in the behavior.

Reviewed-by: Gregory Greenman <gregory.greenman@intel.com>
Reviewed-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>