drm: bridge: dw-hdmi: Rename CONF0 SPARECTRL bit to SVSRET

The bit is documented in a Rockchip BSP as

 #define m_SVSRET_SIG		(1 << 5) /* depend on PHY_MHL_COMB0=1 */

This is confirmed by a Renesas platform, which uses a 2.0 DWC HDMI TX as
the RK3288. Rename the bit accordingly.

Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Reviewed-by: Jose Abreu <joabreu@synopsys.com>
Signed-off-by: Archit Taneja <architt@codeaurora.org>
Link: http://patchwork.freedesktop.org/patch/msgid/20170117082910.27023-13-laurent.pinchart+renesas@ideasonboard.com