cpu/x86/smm_stub.S: Fix comment

The comment got stale because a few elements from the struct got
dropped.

Change-Id: I83469e24dfab82b9182accb549960dd06d81e02f
Signed-off-by: Arthur Heymans <arthur@aheymans.xyz>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/68894
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Kyösti Mälkki <kyosti.malkki@gmail.com>

src/cpu/x86/smm/smm_stub.S

@@ -238,7 +238,7 @@ apicid_end:
 
 	/* Call into the c-based SMM relocation function with the platform
 	 * parameters. Equivalent to:
-	 *   struct arg = { c_handler_params, cpu_num, smm_runtime, canary };
+	 *   struct arg = { cpu_num, canary };
 	 *   c_handler(&arg)
 	 */
 #if ENV_X86_64