nv_alpha_to_coverage_dither_control: Fix equality check.

Fix defect reported by Coverity Scan.

Logically dead code (DEADCODE) dead_error_condition: The condition enable_dither & visualize & (num_samples = 0) cannot be true.

Fixes: 8ea4dcbd ("tests: Added tests for nv_alpha_to_coverage_dither_control") Signed-off-by: Vinson Lee vlee@freedesktop.org