Merge tag 'mailbox-fixes-6.4-rc5' of git://git.linaro.org/landing-teams/working/fujitsu/integration

Pull mailbox fix from Jassi Brar:
 "Fix missing mutex unlock in mailbox-test"

* tag 'mailbox-fixes-6.4-rc5' of git://git.linaro.org/landing-teams/working/fujitsu/integration:
  mailbox: mailbox-test: fix a locking issue in mbox_test_message_write()