drm/omap: fix modeset_init if a panel doesn't satisfy omapdrm requirements

modeset_init iterates through all the registered omapdss devices and has some
initial checks to see if the panel has a driver and the required driver ops for
it to be usable by omapdrm.

The function bails out from modeset_init if a panel doesn't meet the
requirements, and stops the registration of the future panels and encoders which
come after it, that isn't the correct thing to do, we should go through the rest
of the panels. Replace the 'return's with 'continue's.

Signed-off-by: Archit Taneja <archit@ti.com>
Reviewed-by: Rob Clark <robdclark@gmail.com>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>