draw_indirect dEQP failures on a5xx

The following dEQP tests fail on a5xx:

dEQP-GLES31.functional.draw_indirect.compute_interop.large.drawelements_separate_grid_500x500_drawcount_8
dEQP-GLES31.functional.draw_indirect.compute_interop.large.drawelements_separate_grid_500x500_drawcount_2500
dEQP-GLES31.functional.draw_indirect.compute_interop.large.drawarrays_separate_grid_500x500_drawcount_2500
dEQP-GLES31.functional.draw_indirect.compute_interop.large.drawarrays_combined_grid_500x500_drawcount_2500
dEQP-GLES31.functional.draw_indirect.compute_interop.large.drawelements_combined_grid_500x500_drawcount_8
dEQP-GLES31.functional.draw_indirect.compute_interop.large.drawelements_combined_grid_500x500_drawcount_2500

The calculation of the number of elements for indirect draw is wrong, the offset is being subtracted from the dispatch size. This is wrong because size is the absolute number of elements to draw and is independent from the offset.

A similar fix was submitted for a6xx at 79180a05.