hpsa: correct transfer length for 6 byte read/write commands

hpsa: correct transfer length for 6 byte read/write commands

handle block counts of 0. Cleanup block and block count calculations.

Reviewed-by: Scott Teel <[email protected]>
Reviewed-by: Justin Lindley <[email protected]>
Reviewed-by: Kevin Barnett <[email protected]>
Reviewed-by: Tomas Henzl <[email protected]>
Reviewed-by: Hannes Reinecke <[email protected]>
Signed-off-by: Don Brace <[email protected]>
Signed-off-by: Martin K. Petersen <[email protected]>