staging: comedi: avoid memleak for subdevice private

`comedi_alloc_spriv()` allocates private storage for a comedi subdevice
and sets the `SRF_FREE_SPRIV` flag in the `runflags` member of the
subdevice to allow the private storage to be automatically freed when
the comedi device is being cleaned up.  Unfortunately, the flag gets
clobbered by `do_cmd_ioctl()` which calls
`comedi_set_subdevice_runflags()` with a mask value `~0` and only the
`SRF_USER` and `SRF_RUNNING` flags set, all the other SRF flags being
cleared.

Change the calls to `comedi_set_subdevice_runflags()` that currently use
a mask value of `~0` to use a more relevant mask value.  For
`do_cmd_ioctl()`, the relevant SRF flags are `SRF_USER`, `SRF_ERROR` and
`SRF_RUNNING`.  (At one time, `SRF_RT` would be included in that set of
flags, but it is no longer used.)  For `comedi_alloc_spriv()` replace
the call to `comedi_set_subdevice_runflags()` with a simple
OR-assignment to avoid unnecessary use of a spin-lock.
Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
Cc: <stable@vger.kernel.org> # 3.11.y
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/comedi/comedi_fops.c

@@ -543,7 +543,7 @@ void *comedi_alloc_spriv(struct comedi_subdevice *s, size_t size)
 {
 	s->private = kzalloc(size, GFP_KERNEL);
 	if (s->private)
-		comedi_set_subdevice_runflags(s, ~0, SRF_FREE_SPRIV);
+		s->runflags |= SRF_FREE_SPRIV;
 	return s->private;
 }
 EXPORT_SYMBOL_GPL(comedi_alloc_spriv);
@@ -1475,7 +1475,8 @@ static int do_cmd_ioctl(struct comedi_device *dev,
 	if (async->cmd.flags & TRIG_WAKE_EOS)
 		async->cb_mask |= COMEDI_CB_EOS;
 
-	comedi_set_subdevice_runflags(s, ~0, SRF_USER | SRF_RUNNING);
+	comedi_set_subdevice_runflags(s, SRF_USER | SRF_ERROR | SRF_RUNNING,
+				      SRF_USER | SRF_RUNNING);
 
 	/* set s->busy _after_ setting SRF_RUNNING flag to avoid race with
 	 * comedi_read() or comedi_write() */