ARM: OMAP2+: only WARN if a GPMC child probe function fail

If any of the GPMC child nodes fails, this shouldn't make the
whole gpmc_probe_dt() function to fail. It is better to just
WARN and allow other devices probe function to succeed.

Signed-off-by: Javier Martinez Canillas <javier.martinez@collabora.co.uk>
Signed-off-by: Jon Hunter <jon-hunter@ti.com>