ide: __ide_dma_end() -> ide_dma_end()

While at it:
- use EXPORT_SYMBOL_GPL() to match the rest of SFF DMA functions

Acked-by: Sergei Shtylyov <sshtylyov@ru.mvista.com>
Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>