drm: of: simplify component probe code

Use positive logic for better readability. This also eliminates one
of_node_put() call, making the code shorter.

Signed-off-by: Baruch Siach <baruch@tkos.co.il>
Reviewed-by: Philipp Zabel <p.zabel@pengutronix.de>
Tested-by: Philipp Zabel <p.zabel@pengutronix.de>
Signed-off-by: Archit Taneja <archit@cradlewise.com>
Link: https://patchwork.freedesktop.org/patch/msgid/61c56895d44117d80e7d82f04e729e29c60fadbd.1519327370.git.baruch@tkos.co.il