sw/vec: Increase heap size to 1.25M

Latest IREE change caused heap for mobilenet_v1 to increase over 1M and
cause a panic. Increase heap size to account for this.

Bug: 258243964
Fix: 258243964
Change-Id: I41a2f66ecf62b6942a9f12bf0ee81eda068ab572
1 file changed