drm: omapdrm: hdmi: Rename functions and structures to use hdmi_ prefix

The dsi_pll_ops structure and dsi_init_pll_data() function incorrectly
use a dsi_ prefix, likely due to copy & paste. Fix it by using the
correct hdmi_ prefix.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>