drm/sun4i: Fix sun8i HDMI PHY configuration for > 148.5 MHz

Vendor provided documentation says that EMP bits should be set to 3 for
pixel clocks greater than 148.5 MHz.

Fix that.

Cc: stable@vger.kernel.org # 4.17+
Fixes: 4f86e817 ("drm/sun4i: Add support for H3 HDMI PHY variant")
Signed-off-by: Jernej Skrabec <jernej.skrabec@siol.net>
Signed-off-by: Maxime Ripard <maxime.ripard@bootlin.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190514204337.11068-3-jernej.skrabec@siol.net