amdgpu/dce11: Remove division from dce_v11_0_vblank_wait()

Mimics odd behaviour where (i++ % 100 == 0) is true in the first iteration of each loop...

Signed-off-by: Tom St Denis <tom.stdenis@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>