cs5536: define dma_sff_read_status() method

The driver somehow got merged with the initializer for the dma_sff_read_status()
method missing which caused kernel panic on bootup.

This should fix the kernel.org bug #13026...

Signed-off-by: Sergei Shtylyov <sshtylyov@ru.mvista.com>
Reported-by: Arnd Hannemann <hannemann@nets.rwth-aachen.de>
Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>