freedreno/a5xx: Fix indirect draw max_indices calculation

The number of elements to draw should not be affected by the offset.

A similar fix was submitted for a6xx at 79180a05.

Fixes these dEQP tests 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

Reviewed-by: Rob Clark <robdclark@gmail.com>
(cherry picked from commit 3fb7b1fd)