comedi: drivers: ni_tio: Fix slightly broken kernel-doc and demote others

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

drivers/staging/comedi/drivers/ni_tio.c:1515: warning: Function parameter or member 'counter_dev' not described in 'ni_tio_get_routing'
drivers/staging/comedi/drivers/ni_tio.c:1515: warning: Function parameter or member 'dest' not described in 'ni_tio_get_routing'
drivers/staging/comedi/drivers/ni_tio.c:1515: warning: expecting prototype for Retrieves the register value of the current source of the output selector for(). Prototype was for ni_tio_get_routing() instead
drivers/staging/comedi/drivers/ni_tio.c:1544: warning: This comment starts with '/**', but isn't a kernel-doc comment. Refer Documentation/doc-guide/kernel-doc.rst
drivers/staging/comedi/drivers/ni_tio.c:1584: warning: This comment starts with '/**', but isn't a kernel-doc comment. Refer Documentation/doc-guide/kernel-doc.rst

Cc: Ian Abbott <[e-mail]>
Cc: H Hartley Sweeten <[e-mail]>
Cc: Greg Kroah-Hartman <[e-mail]>
Cc: Mori Hess <[e-mail]>
Cc: "J.P. Mellor" <[e-mail]>
Cc: [e-mail]
Cc: [e-mail]
Cc: [e-mail]
Cc: Comedi <[e-mail]>
Cc: [e-mail]
Signed-off-by: Lee Jones <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/comedi/drivers/ni_tio.c

···
 }
 EXPORT_SYMBOL_GPL(ni_tio_insn_config);
 
-/**
+/*
  * Retrieves the register value of the current source of the output selector for
  * the given destination.
  *
···
 EXPORT_SYMBOL_GPL(ni_tio_get_routing);
 
 /**
- * Sets the register value of the selector MUX for the given destination.
- * @counter_dev:Pointer to general counter device.
- * @destination:Device-global identifier of route destination.
- * @register_value:
+ * ni_tio_set_routing() - Sets the register value of the selector MUX for the given destination.
+ * @counter_dev: Pointer to general counter device.
+ * @dest:        Device-global identifier of route destination.
+ * @reg:
  *		The first several bits of this value should store the desired
  *		value to write to the register.  All other bits are for
  *		transmitting information that modify the mode of the particular
···
 }
 EXPORT_SYMBOL_GPL(ni_tio_set_routing);
 
-/**
+/*
  * Sets the given destination MUX to its default value or disable it.
  *
  * Return: 0 if successful; -EINVAL if terminal is unknown.