net: dsa: Fix possible memory leaks in dsa_loop_init()

Summary

In the Linux kernel, the following vulnerability has been resolved: net: dsa: Fix possible memory leaks in dsa_loop_init() kmemleak reported memory leaks in dsa_loop_init(): kmemleak: 12 new suspected memory leaks unreferenced object 0xffff8880138ce000 (size 2048): comm "modprobe", pid 390, jiffies 4295040478 (age 238.976s) backtrace: [<000000006a94f1d5>] kmalloc_trace+0x26/0x60 [<00000000a9c44622>] phy_device_create+0x5d/0x970 [<00000000d0ee2afc>] get_phy_device+0xf3/0x2b0 [<00000000dca0c71f>] __fixed_phy_register.part.0+0x92/0x4e0 [<000000008a834798>] fixed_phy_register+0x84/0xb0 [<0000000055223fcb>] dsa_loop_init+0xa9/0x116 [dsa_loop] ... There are two reasons for memleak in dsa_loop_init(). First, fixed_phy_register() create and register phy_device: fixed_phy_register() get_phy_device() phy_device_create() # freed by phy_device_free() phy_device_register() # freed by phy_device_remove() But fixed_phy_unregister() only calls phy_device_remove(). So the memory allocated in phy_device_create() is leaked. Second, when mdio_driver_register() fail in dsa_loop_init(), it just returns and there is no cleanup for phydevs. Fix the problems by catching the error of mdio_driver_register() in dsa_loop_init(), then calling both fixed_phy_unregister() and phy_device_free() to release phydevs. Also add a function for phydevs cleanup to avoid duplacate.