When auxiliary_device_add() returns error and then calls
auxiliary_device_uninit(), callback function adev_release
calls kfree(madev). We shouldn't call kfree(madev) again
in the error handling path. Set 'madev' to NULL.

Fixes: a69839d4 ("net: mana: Add support for auxiliary device")
Signed-off-by: Ma Ke <make24@iscas.ac.cn>
Link: https://patch.msgid.link/20240625130314.2661257-1-make24@iscas.ac.cnSigned-off-by: Paolo Abeni <pabeni@redhat.com>