Description: usb: usbtest: fix missing kfree(dev->buf) in usbtest_disconnect
References:
 https://lkml.org/lkml/2020/6/2/968
Notes:
 carnil> releases as well in 5.7.8.
Bugs:
upstream: released (5.8-rc3) [28ebeb8db77035e058a510ce9bd17c2b9a009dba]
4.19-upstream-stable: released (4.19.132) [7b0f1f89a0dd6e257367eddc840179e85195ca18]
4.9-upstream-stable: released (4.9.230) [4ea5c9091d62e9516819c7bcb7c09658bde85acc]
sid: released (5.7.10-1)
4.19-buster-security: released (4.19.131-1) [bugfix/all/usb-usbtest-fix-missing-kfree-dev-buf-in-usbtest_dis.patch]
4.9-stretch-security: released (4.9.240-1)