s390/cio: fix kdoc for tiqdio_thinint_handler

Add missing parameter description to fix the following warning:
drivers/s390/cio/qdio_thinint.c:183: warning:
Function parameter or member 'floating' not described in 'tiqdio_thinint_handler'

Signed-off-by: Sebastian Ott <sebott@linux.ibm.com>
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>