staging: kpc2000: use __func__ in debug messages

Fixes checkpatch.pl warning "Prefer using '"%s...", __func__' to using
'<function name>', this function's name, in a string".

Signed-off-by: Simon Sandström <simon@nikanor.nu>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>