[SCSI] megaraid_sas: return sync cache call with success

FW does not support SYNCHRONIZE_CACHE cmd. FW flush cache on its own.
So, we just return success from the megasas_queue_command.

Signed-off-by: Sumant Patro <sumant.patro@lsi.com>
Signed-off-by: James Bottomley <James.Bottomley@SteelEye.com>