drm/i915: completely reset the value of DDI_FUNC_CTL

Don't rely on previous values already set on the register. Everything
we're not explicitly setting should be zero for now.
Signed-off-by: NPaulo Zanoni <paulo.r.zanoni@intel.com>
Reviewed-by: NJani Nikula <jani.nikula@intel.com>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/intel_ddi.c

@@ -723,12 +723,7 @@ void intel_ddi_mode_set(struct drm_encoder *encoder,
 	}
 
 	/* Enable PIPE_DDI_FUNC_CTL for the pipe to work in HDMI mode */
-	temp = I915_READ(DDI_FUNC_CTL(pipe));
-	temp &= ~PIPE_DDI_PORT_MASK;
-	temp &= ~PIPE_DDI_BPC_MASK;
-	temp &= ~PIPE_DDI_MODE_SELECT_MASK;
-	temp &= ~(PIPE_DDI_PVSYNC | PIPE_DDI_PHSYNC);
-	temp |= PIPE_DDI_FUNC_ENABLE | PIPE_DDI_SELECT_PORT(port);
+	temp = PIPE_DDI_FUNC_ENABLE | PIPE_DDI_SELECT_PORT(port);
 
 	switch (intel_crtc->bpp) {
 	case 18: