Description: p54usb: Fix race between disconnect and firmware loading
References:
 https://syzkaller.appspot.com/bug?id=082c09653e43e33a6a56f8c57cf051eeacae9d5f
Notes:
 bwh> Probably introduced in 3.5 by commit 5612a508d11f "p54usb: Load firmware
 bwh> asynchronously".
Bugs:
upstream: released (5.3-rc1) [6e41e2257f1094acc37618bf6c856115374c6922]
4.19-upstream-stable: released (4.19.59) [449a8d08a4bc45101fa26e6d233b98258d33620a]
4.9-upstream-stable: released (4.9.186) [feca0ce34518f69447d0d13cd431d0eef647a794]
3.16-upstream-stable: released (3.16.74) [450e350ba7c383dc74b181e4eeb50526df68433e]
sid: released (5.2.6-1)
4.19-buster-security: released (4.19.67-1)
4.9-stretch-security: released (4.9.189-1)
3.16-jessie-security: released (3.16.74-1)