rapidio: change to new flag variable

switches/ depends on RAPIDIO_DEBUG so the subdir-ccflags-y variant
seems to be appropriate here.

Signed-off-by: matt mooney <mfm@muteddisk.com>
Acked-by: WANG Cong <xiyou.wangcong@gmail.com>
Signed-off-by: Michal Marek <mmarek@suse.cz>