arm_pmu: acpi: handle allocation failure

One of the failure paths in the arm_pmu ACPI code is missing an early
return, permitting a NULL pointer dereference upon a memory allocation
failure.

Add the missing return.

Fixes: fe40ffdb ("arm_pmu: rework ACPI probing")
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Reported-by: Will Deacon <will@kernel.org>
Link: https://lore.kernel.org/r/20221108093725.1239563-1-mark.rutland@arm.comSigned-off-by: Will Deacon <will@kernel.org>

drivers/perf/arm_pmu_acpi.c

@@ -333,6 +333,7 @@ int arm_pmu_acpi_probe(armpmu_init_fn init_fn)
 		if (!pmu) {
 			pr_warn("Unable to allocate PMU for CPU%d\n",
 				cpu);
+			return -ENOMEM;
 		}
 
 		cpuid = per_cpu(cpu_data, cpu).reg_midr;