drm/tilcdc: fix parsing of some DT properties

The DT binding for tildc is not consistent with the driver code: there
are two options - 'max-width' and 'max-pixelclock' specified in the
documentation which are parsed as 'ti,max-width' and
'ti,max-pixelclock' respectively.

Make the driver code consistent with the binding.

Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>
Reviewed-by: Jyri Sarha <jsarha@ti.com>
Signed-off-by: Jyri Sarha <jsarha@ti.com>