Merge remote-tracking branch 'remotes/kraxel/tags/usb-20190307-pull-request' into staging

usb: mtp fixes, guest-reset switch for usb-host.

# gpg: Signature made Thu 07 Mar 2019 09:53:55 GMT
# gpg:                using RSA key 4CB6D8EED3E87138
# gpg: Good signature from "Gerd Hoffmann (work) <kraxel@redhat.com>" [full]
# gpg:                 aka "Gerd Hoffmann <gerd@kraxel.org>" [full]
# gpg:                 aka "Gerd Hoffmann (private) <kraxel@gmail.com>" [full]
# Primary key fingerprint: A032 8CFF B93A 17A7 9901  FE7D 4CB6 D8EE D3E8 7138

* remotes/kraxel/tags/usb-20190307-pull-request:
  Introduce new "no_guest_reset" parameter for usb-host device
  usb-mtp: prevent null dereference while deleting objects
  usb-mtp: fix some usb_mtp_write_data return paths
  usb-mtp: return incomplete transfer on a lstat failure

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>