drm: bridge: dw-hdmi: Remove unused function parameter

The 'prep' parameter passed to hdmi_phy_configure() is useless. It is
hardcoded as 0, and if set, simply prevents the configure function from
executing.

Remove it.

Signed-off-by: Kieran Bingham <kieran.bingham+renesas@ideasonboard.com>
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/20170117082910.27023-4-laurent.pinchart+renesas@ideasonboard.com