comedi: drivers: comedi_isadma: Fix misspelling of 'dma_chan1'

comedi: drivers: comedi_isadma: Fix misspelling of 'dma_chan1'

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

 drivers/staging/comedi/drivers/comedi_isadma.c:157: warning: Function parameter or member 'dma_chan1' not described in 'comedi_isadma_alloc'
 drivers/staging/comedi/drivers/comedi_isadma.c:157: warning: Excess function parameter 'dma_chan' description in 'comedi_isadma_alloc'

Cc: Ian Abbott <abbotti@mev.co.uk>
Cc: H Hartley Sweeten <hsweeten@visionengravers.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: linux-staging@lists.linux.dev
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Link: https://lore.kernel.org/r/20210520122538.3470259-7-lee.jones@linaro.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>