comedi: comedi_8254: Fix descriptions for 'i8254' and 'iobase'

comedi: comedi_8254: Fix descriptions for 'i8254' and 'iobase'

Fixes the following W=1 kernel build warning(s):

 drivers/staging/comedi/drivers/comedi_8254.c:561: warning: Function parameter or member 'i8254' not described in 'comedi_8254_subdevice_init'
 drivers/staging/comedi/drivers/comedi_8254.c:620: warning: Function parameter or member 'iobase' not described in 'comedi_8254_init'
 drivers/staging/comedi/drivers/comedi_8254.c:620: warning: Excess function parameter 'mmio' description in 'comedi_8254_init'

Cc: Ian Abbott <abbotti@mev.co.uk>
Cc: H Hartley Sweeten <hsweeten@visionengravers.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: "David A. Schleef" <ds@schleef.org>
Cc: linux-staging@lists.linux.dev
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Link: https://lore.kernel.org/r/20210520122538.3470259-2-lee.jones@linaro.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>