drm/meson: Fix some error handling paths in 'meson_drv_bind_master()'

If one of these functions fail, we whould free 'drm', as alreadry done in
the other error handling paths, below and above.

Fixes: bbbe775e

 ("drm: Add support for Amlogic Meson Graphic Controller")
Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Acked-by: Neil Armstrong <narmstrong@baylibre.com>
Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Link: https://patchwork.freedesktop.org/patch/msgid/df47e03d36c2cf7bc37ec3105fc47c16555bd946.1520885192.git.christophe.jaillet@wanadoo.fr