staging: comedi: dyna_pci10xx: remove set but not used variables 'chan' and range'

Fixes gcc '-Wunused-but-set-variable' warning:

drivers/staging/comedi/drivers/dyna_pci10xx.c: In function 'dyna_pci10xx_insn_write_ao':
drivers/staging/comedi/drivers/dyna_pci10xx.c:109:21: warning:
 variable 'range' set but not used [-Wunused-but-set-variable]
  unsigned int chan, range;

drivers/staging/comedi/drivers/dyna_pci10xx.c:109:15: warning:
 variable 'chan' set but not used [-Wunused-but-set-variable]
  unsigned int chan, range;

They are never used since introduction in commit 16a7373a ("Staging:
comedi: add dyna_pci10xx driver")
Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Reviewed-by: Ian Abbott <abbotti@mev.co.uk>
Reviewed-by: Mukesh Ojha <mojha@codeaurora.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/comedi/drivers/dyna_pci10xx.c

@@ -106,10 +106,6 @@ static int dyna_pci10xx_insn_write_ao(struct comedi_device *dev,
 {
 	struct dyna_pci10xx_private *devpriv = dev->private;
 	int n;
-	unsigned int chan, range;
-
-	chan = CR_CHAN(insn->chanspec);
-	range = range_codes_pci1050_ai[CR_RANGE((insn->chanspec))];
 
 	mutex_lock(&devpriv->mutex);
 	for (n = 0; n < insn->n; n++) {