iwmc3200wifi: check for iwm_priv_init error

We need to check for iwm_priv_init() errors and do proper cleanups.
Otherwise we may fail to catch the create_singlethread_workqueue()
error which will cause a kernel oops when destroy_workqueue() later.

Signed-off-by: Zhu Yi <yi.zhu@intel.com>
Signed-off-by: Samuel Ortiz <samuel.ortiz@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>