platform/x86: dell-wmi-sysman: fix init_bios_attributes() error handling

Calling release_attributes_data() while holding the "wmi_priv.mutex"
will lead to a dead lock.  The other problem is that if kzalloc() fails
then this should return -ENOMEM but currently it returns success.

Fixes: e8a60aa7

 ("platform/x86: Introduce support for Systems Management Driver over WMI for Dell Systems")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Link: https://lore.kernel.org/r/20201103101735.GB1127762@mwanda
Signed-off-by: Hans de Goede <hdegoede@redhat.com>