edid: fix edid_get_timing_validate() mode_valid lookup

Add a condition to the break in the modes lookup, without this
when the first mode is not valid, then edid_get_timing_validate()
return an error instead of checking the next modes.

Fixes: 1c1ed441 ("edid: add edid_get_timing_validate() variant to filter out edid modes")
Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>