drm/msm: perform mode fixup against current state

Current mode fixup validates mode against both state mode and crtc mode
which causes mismatch between validation and drm_mode_equal check.
Perform validation against the same mode (crtc->state->mode) to avoid
mismatch and reflect proper state.

Change-Id: If5647f2df0275cc14dd8d761d16e58fd0aa775f7
Signed-off-by: Adrian Salido <salidoa@google.com>
Signed-off-by: Lakshmi Narayana Kalavala <lkalaval@codeaurora.org>