libata: Fix build failure on ppc64 drivers/ata/pata_scc.c

Little fixlets, that the build started erroring / warning about:

drivers/ata/pata_scc.c: In function 'scc_bmdma_status':
drivers/ata/pata_scc.c:734: error: structure has no member named 'active_tag'
drivers/ata/pata_scc.c: In function 'scc_pata_prereset':
drivers/ata/pata_scc.c:866: warning: passing arg 1 of 'ata_std_prereset' from incompatible pointer type
drivers/ata/pata_scc.c: In function 'scc_error_handler':
drivers/ata/pata_scc.c:908: warning: passing arg 2 of 'ata_bmdma_drive_eh' from incompatible pointer type
drivers/ata/pata_scc.c:908: warning: passing arg 3 of 'ata_bmdma_drive_eh' from incompatible pointer type
drivers/ata/pata_scc.c:908: warning: passing arg 5 of 'ata_bmdma_drive_eh' from incompatible pointer type
make[2]: *** [drivers/ata/pata_scc.o] Error 1

Signed-off-by: Satyam Sharma <satyam@infradead.org>
Cc: Alan Cox <alan@redhat.com>
Cc: Mel Gorman <mel@skynet.ie>
Signed-off-by: Jeff Garzik <jeff@garzik.org>