staging: wfx: fix an error handling in wfx_init_common()

In the Linux kernel, the following vulnerability has been resolved: staging: wfx: fix an error handling in wfx_init_common() One error handler of wfx_init_common() return without calling ieee80211_free_hw(hw), which may result in memory leak. And I add one err label to unify the error handler, which is useful for the subsequent changes.