wifi: iwlwifi: pcie: add size assertions

Ensure that the TX command scratch fits into the buffer
provided by the first TB. It does, of course, but add
some build-time validations in case we touch this code.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Gregory Greenman <gregory.greenman@intel.com>
Link: https://lore.kernel.org/r/20230620125813.8f54f2990b92.If19a038dfd633d4601e3d44dd0ff678bc0a851e9@changeid


Signed-off-by: Johannes Berg <johannes.berg@intel.com>