target/rd: T10-Dif: RAM disk is allocating more space than required.

target/rd: T10-Dif: RAM disk is allocating more space than required.

commit 9d2e59f2a778328a41771fe9a0098dadbc4314ba upstream.

Ram disk is allocating 8x more space than required for diff data.
For large RAM disk test, there is small potential for memory
starvation.

(Use block_size when calculating total_sg_needed - sagi + nab)

Signed-off-by: Giridhar Malavali <giridhar.malavali@qlogic.com>
Signed-off-by: Quinn Tran <quinn.tran@qlogic.com>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>