drivers/char/dsp56k.c: drop check for negativity of unsigned parameter

[linux-3.16-rc5/drivers/char/dsp56k.c:386]: (style) Checking if unsigned
variable 'arg' is less than zero.

Source code is

            if (arg > 31 || arg < 0)
                return -EINVAL;

But

static long dsp56k_ioctl(struct file *file, unsigned int cmd,
             unsigned long arg)

Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=80411


Reported-by: David Binderman <dcb314@hotmail.com>
Signed-off-by: Andrey Utkin <andrey.krieger.utkin@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>