drm/sun4i: Fix dclk_set_phase

Phase value is not shifted before writing.

Shift left of 28 bits to fit right bits

Signed-off-by: Giulio Benetti <giulio.benetti@micronovasrl.com>
Signed-off-by: Maxime Ripard <maxime.ripard@bootlin.com>
Link: https://patchwork.freedesktop.org/patch/msgid/1519836413-35023-1-git-send-email-giulio.benetti@micronovasrl.com