drm/amd/display: optimize code runtime a bit

In fnction is_cr_done & is_ch_eq_done, when done = false
happened once, no need to circle left ln_count.
This change is to make the code run a bit fast.

Signed-off-by: Bernard Zhao <bernard@vivo.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>