drm/msm/dp: clear scrambler bypass for test pattern 4

Clear the scrambler bypass bit while programming test pattern 4
for electrical compliance. This bit is only used for debugging
purposes and must be unset in order to get the correct test pattern
output from the controller.

Change-Id: If54ba17dc5bdd096899cf57cc4f276aab1837308
Signed-off-by: RAJAT GUPTA <rajatgu@codeaurora.org>