staging: comedi: comedi_fops.c: reformat ioctl handler comments

The unlocked_ioctl handler calls a different function to handle each
supported ioctl command code.  Most of these have a block comment
indicating which command code it handles, a brief description, and an
informal description of the inputs and outputs.  These block comments
are formatted in various styles.  Reformat them to the usual block
comment style and do a bit of rewording for consistency.  The comment
block for the `COMEDI_CMD` ioctl is missing, so add one.

Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
Reviewed-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>