USB: iowarrior: drop redundant iowarrior mutex

Drop the redundant iowarrior mutex introduced by commit 925ce689
("USB: autoconvert trivial BKL users to private mutex") which replaced
an earlier BKL use.

The lock serialised calls to open() against other open() and ioctl(),
but neither is needed.

Signed-off-by: Johan Hovold <johan@kernel.org>
Link: https://lore.kernel.org/r/20191009104846.5925-6-johan@kernel.org


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>