drm/udl: Support adapters without firmware descriptor

Set default limit on the number of pixels for adapters without
vendor firmware descriptor. The devices work as expected, they
just don't provide any description.

If parsing the vendor firmware descriptor fails, the device falls
back to the given default limits. Failing to allocate memory is
still an error.

v2:
- fix typo in constant (Patrik)

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Patrik Jakobsson <patrik.r.jakobsson@gmail.com>
Link: https://lore.kernel.org/r/20250410105948.25463-10-tzimmermann@suse.de