drm/sun4i: hdmi: Fix an error handling path in 'sun4i_hdmi_bind()'

If we can not allocate the HDMI encoder regmap, we still need to free some
resources before returning.

Fixes: 4b1c924b

 ("drm/sun4i: hdmi: create a regmap for later use")
Reviewed-by: Chen-Yu Tsai <wens@csie.org>
Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Signed-off-by: Maxime Ripard <maxime.ripard@bootlin.com>
Link: https://patchwork.freedesktop.org/patch/msgid/14c42391e1b562c7495bda6ad6fa1d24ec8dc052.1521413031.git.christophe.jaillet@wanadoo.fr