net: thunderbolt: Fix error handling in tbnet_init()

A problem about insmod thunderbolt-net failed is triggered with following
log given while lsmod does not show thunderbolt_net:

 insmod: ERROR: could not insert module thunderbolt-net.ko: File exists

The reason is that tbnet_init() returns tb_register_service_driver()
directly without checking its return value, if tb_register_service_driver()
failed, it returns without removing property directory, resulting the
property directory can never be created later.

 tbnet_init()
   tb_register_property_dir() # register property directory
   tb_register_service_driver()
     driver_register()
       bus_add_driver()
         priv = kzalloc(...) # OOM happened
   # return without remove property directory

Fix by remove property directory when tb_register_service_driver() returns
error.

Fixes: e69b6c02

 ("net: Add support for networking over Thunderbolt cable")
Signed-off-by: Yuan Can <yuancan@huawei.com>
Acked-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>