arm64: cpufeature: move to use bus_get_dev_root()

Direct access to the struct bus_type dev_root pointer is going away soon
so replace that with a call to bus_get_dev_root() instead, which is what
it is there for.

Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will@kernel.org>
Cc: Mark Brown <broonie@kernel.org>
Cc: James Morse <james.morse@arm.com>
Cc: Kristina Martsenko <kristina.martsenko@arm.com>
Cc: Marc Zyngier <maz@kernel.org>
Cc: Ard Biesheuvel <ardb@kernel.org>
Cc: Vladimir Murzin <vladimir.murzin@arm.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: linux-arm-kernel@lists.infradead.org
Link: https://lore.kernel.org/r/20230313182918.1312597-11-gregkh@linuxfoundation.orgSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

arch/arm64/kernel/cpufeature.c

@@ -1490,10 +1490,18 @@ static const DEVICE_ATTR_RO(aarch32_el0);
 
 static int __init aarch32_el0_sysfs_init(void)
 {
+	struct device *dev_root;
+	int ret = 0;
+
 	if (!allow_mismatched_32bit_el0)
 		return 0;
 
-	return device_create_file(cpu_subsys.dev_root, &dev_attr_aarch32_el0);
+	dev_root = bus_get_dev_root(&cpu_subsys);
+	if (dev_root) {
+		ret = device_create_file(dev_root, &dev_attr_aarch32_el0);
+		put_device(dev_root);
+	}
+	return ret;
 }
 device_initcall(aarch32_el0_sysfs_init);