ide: remove wmb() from ide-dma-sff.c and scc_pata.c

This patch:
o replaces "mask" variable in ide_dma_end() with #define.
o removes use of wmb() in ide-dma-sff.c and scc_pata.c.
o is not tested - I don't have (or want) the HW.

Signed-off-by: Grant Grundler <grundler@google.com>
Cc: KOBAYASHI Yoshitake <yoshitake.kobayashi@toshiba.co.jp>
Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>