drm: msm: dsi-staging: update the crtc value in mode fixup

crtc is taken from bridge->encoder which doesnot have a mutex
lock protection. This resulted in race condition where
bridge->encoder->crtc becomes NULL within the null check
condition. The change takes crtc from crtc_state to avoid this.

Change-Id: Icaf224d944eaf91a25e011a897c93973bada29d5
Signed-off-by: Raviteja Tamatam <travitej@codeaurora.org>