staging: rtl8712: error handling refactoring

commit e9e6aa51 upstream.

There was strange error handling logic in case of fw load failure. For
some reason fw loader callback was doing clean up stuff when fw is not
available. I don't see any reason behind doing this. Since this driver
doesn't have EEPROM firmware let's just disconnect it in case of fw load
failure. Doing clean up stuff in 2 different place which can run
concurently is not good idea and syzbot found 2 bugs related to this
strange approach.

So, in this pacth I deleted all clean up code from fw callback and made
a call to device_release_driver() under device_lock(parent) in case of fw
load failure. This approach is more generic and it defend driver from UAF
bugs, since all clean up code is moved to one place.

Fixes: e02a3b94 ("staging: rtl8712: fix memory leak in rtl871x_load_fw_cb")
Fixes: 8c213fa5

 ("staging: r8712u: Use asynchronous firmware loading")
Cc: stable <stable@vger.kernel.org>
Reported-and-tested-by:  <syzbot+5872a520e0ce0a7c7230@syzkaller.appspotmail.com>
Reported-and-tested-by:  <syzbot+cc699626e48a6ebaf295@syzkaller.appspotmail.com>
Signed-off-by: Pavel Skripkin <paskripkin@gmail.com>
Link: https://lore.kernel.org/r/d49ecc56e97c4df181d7bd4d240b031f315eacc3.1626895918.git.paskripkin@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>