staging: comedi: ni_labpc: unlock spinlock on command error

When starting the acquisition the labpc_ai_cmd function was
exiting without unlocking the spinlock. This results in a
sparse warning:

warning: context imbalance in 'labpc_ai_cmd' - different lock contexts for basic block

Add the missing spin_unlock_irqrestore calls.
Signed-off-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Cc: Ian Abbott <abbotti@mev.co.uk>
Cc: Mori Hess <fmhess@users.sourceforge.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/comedi/drivers/ni_labpc.c

@@ -1386,6 +1386,7 @@ static int labpc_ai_cmd(struct comedi_device *dev, struct comedi_subdevice *s)
 		break;
 	default:
 		comedi_error(dev, "bug with start_src");
+		spin_unlock_irqrestore(&dev->spinlock, flags);
 		return -1;
 		break;
 	}
@@ -1398,6 +1399,7 @@ static int labpc_ai_cmd(struct comedi_device *dev, struct comedi_subdevice *s)
 		break;
 	default:
 		comedi_error(dev, "bug with stop_src");
+		spin_unlock_irqrestore(&dev->spinlock, flags);
 		return -1;
 	}
 	devpriv->write_byte(devpriv->command2_bits, dev->iobase + COMMAND2_REG);