drm/i915/vblank: Make the vblank counter u64 -> u32 typecast explicit

Core returns a u64 vblank count and intel_crtc_get_vblank_counter()
expects a 32-bit value. Make the typecast explicit to add clarity.

Cc: Keith Packard <keithp@keithp.com>
Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: Dhinakaran Pandiyan <dhinakaran.pandiyan@intel.com>
Reviewed-by: Keith Packard <keithp@keithp.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180203051302.9974-2-dhinakaran.pandiyan@intel.com

drivers/gpu/drm/i915/intel_display.c

@@ -12078,7 +12078,7 @@ u32 intel_crtc_get_vblank_counter(struct intel_crtc *crtc)
 	struct drm_device *dev = crtc->base.dev;
 
 	if (!dev->max_vblank_count)
-		return drm_crtc_accurate_vblank_count(&crtc->base);
+		return (u32)drm_crtc_accurate_vblank_count(&crtc->base);
 
 	return dev->driver->get_vblank_counter(dev, crtc->pipe);
 }