Revert "drm/amdgpu: Only update the CUR_SIZE register when necessary"

This reverts commits 7c83d7ab and
a1f49cc1.

They caused the HW cursor to disappear under various circumstances in
the wild. I wasn't able to reproduce any of them, and I'm not sure
what's going on. But those changes aren't a big deal anyway, so let's
just revert for now.

Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=191291
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=99143


Acked-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>