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>