wifi: iwlwifi: mvm: use already determined cmd_id

In iwl_mvm_rs_fw_rate_init() we have a variable cmd_id that
holds the command ID, so we can just use that instead of the
various calculations of it.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Miri Korenblit <miriam.rachel.korenblit@intel.com>
Link: https://msgid.link/20240506095953.f894ede03b26.I18f03c272b1c0807767f2713f3ffbb2941c57d9b@changeid
Signed-off-by: Johannes Berg <johannes.berg@intel.com>