media: mt9m111: fix fw-node refactoring

In the patch refactoring the fw-node, the mt9m111 was broken for all
platform_data based platforms, which were the first aim of this
driver. Only the devicetree platform are still functional, probably
because the testing was done on these.

The result is that -EINVAL is systematically return for such platforms,
what this patch fixes.

[Sakari Ailus: Rework this to resolve a merge conflict and use dev_fwnode]

Fixes: 98480d65 ("media: mt9m111: allow to setup pixclk polarity")
Signed-off-by: Robert Jarzmik <robert.jarzmik@free.fr>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>