MLBEDSW-6296: Updated condition for the opt size weight buffering schedule

Allow schedule do be used when calculations says zero total improvement
but calculations on the other hand shows there are dram improvement.
When testing on real target, total performance is improvement.

Signed-off-by: Johan Alfven <johan.alfven@arm.com>
Change-Id: Ib4f2a37710dc7954b72b48c38fce4817ccd7187b