drm: msm: dsi-staging: update dfps validation mode check

Crtc mode is updated in the commit path and this should
not be used for validation of dfps change. Instead,
crtc state mode variable needs to used for dfps validation
which contains latest state.

Change-Id: I6dd1273cc5eac94b11c24afb6d1748369cd73be8
Signed-off-by: Raviteja Tamatam <travitej@codeaurora.org>