cpu/x86/smi_trigger: use enum cb_err as apm_control return type

Even though the return value from apm_control isn't checked at any of
its call sites, using the cb_err enum instead of an integer as return
type makes it clearer what the returned value means.

Signed-off-by: Felix Held <felix-coreboot@felixheld.de>
Change-Id: I07ced74cae915df52a9d439835b84237d51fdd11
Reviewed-on: https://review.coreboot.org/c/coreboot/+/79835
Reviewed-by: Jérémy Compostella <jeremy.compostella@intel.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Eric Lai <ericllai@google.com>
Reviewed-by: Matt DeVillier <matt.devillier@amd.corp-partner.google.com>

src/cpu/x86/smi_trigger.c

@@ -29,11 +29,11 @@ static void apmc_log(const char *fn, u8 cmd)
 	}
 }
 
-int apm_control(u8 cmd)
+enum cb_err apm_control(u8 cmd)
 {
 	/* Never proceed inside SMI handler or without one. */
 	if (ENV_SMM || !CONFIG(HAVE_SMI_HANDLER))
-		return -1;
+		return CB_ERR;
 
 	apmc_log(__func__, cmd);
 
@@ -41,7 +41,7 @@ int apm_control(u8 cmd)
 	outb(cmd, pm_acpi_smi_cmd_port());
 
 	printk(BIOS_DEBUG, "APMC done.\n");
-	return 0;
+	return CB_SUCCESS;
 }
 
 u8 apm_get_apmc(void)

src/include/cpu/x86/smm.h

@@ -43,7 +43,7 @@
 #endif
 
 /* Send cmd to APM_CNT with HAVE_SMI_HANDLER checking. */
-int apm_control(u8 cmd);
+enum cb_err apm_control(u8 cmd);
 u8 apm_get_apmc(void);
 
 void io_trap_handler(int smif);