dmaengine: bcm-sba-raid: Use common GPL comment header

This patch makes the comment header of Broadcom SBA RAID driver
similar to the GPL comment header used across Broadcom driver
sources.

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