drm: samsung: panel: use crtc_state mode instead of current

By using crtc_state->mode instead of ctx->current_mode, the mode will
reflect the latest committed atomic state even if it hasn't been applied
yet (i.e. atomic commit tail still in progress).

Bug: 194407556
Change-Id: I26d0c8645e03d14e5443723a4def7459e404d3d2
Signed-off-by: Adrian Salido <salidoa@google.com>