net: dsa: bcm_sf2: Fix a possible memory leak in bcm_sf2_mdio_register()

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UBUNTU-CVE-2022-48815

In the Linux kernel, the following vulnerability has been resolved: net: dsa: bcmsf2: don't use devres for mdiobus As explained in commits: 74b6d7d13307 "net: dsa: realtek: register the MDIO bus under devres" 5135e96a3dd2 "net: dsa: don't allocate the slavemiibus using devres" mdiobusfree will...