irqchip/gic-v3-its: Fix build for !SMP

Commit 835f442 ("irqchip/gic-v3-its: Limit memreserve cpuhp state
lifetime") added a reference to cpus_booted_once_mask, which does not
exist on !SMP builds, breaking the build for such configurations.

Given the intent of the check, short circuit it to always pass.

Cc: Valentin Schneider <valentin.schneider@arm.com>
Fixes: 835f442 ("irqchip/gic-v3-its: Limit memreserve cpuhp state lifetime")
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20220122151614.133766-1-ardb@kernel.org

drivers/irqchip/irq-gic-v3-its.c

@@ -5241,7 +5241,8 @@ static int its_cpu_memreserve_lpi(unsigned int cpu)
 
 out:
 	/* Last CPU being brought up gets to issue the cleanup */
-	if (cpumask_equal(&cpus_booted_once_mask, cpu_possible_mask))
+	if (!IS_ENABLED(CONFIG_SMP) ||
+	    cpumask_equal(&cpus_booted_once_mask, cpu_possible_mask))
 		schedule_work(&rdist_memreserve_cpuhp_cleanup_work);
 
 	gic_data_rdist()->flags |= RD_LOCAL_MEMRESERVE_DONE;