staging: comedi: Use '"%s:", __func__' instead of function name

Replace an occurrence of the function name in a string by a reference
to __func__, to improve robustness. Problem found with checkpatch.

Signed-off-by: Eisha Chen-yen-su <chenyensu0@gmail.com>
Acked-by: Julia Lawall <julia.lawall@lip6.fr>
Reviewed-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>