dmaengine: bcm-sba-raid: Remove redundant next_count from sba_request

The next_count in sba_request is redundant because same information
is captured by next_pending_count. This patch removes next_count
from sba_request.

Signed-off-by: Anup Patel <anup.patel@broadcom.com>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>