Bluetooth: audio: ascs: Remove invalid check

This fixes invalid check, which is redundant in fact as the length
is already checked in ascs_parse_metadata function.
The check be test 'greater than' only, as 'equal' condition is valid.
Moreover this fixes return value from ascs_verify_metadata function.

Signed-off-by: Mariusz Skamra <mariusz.skamra@codecoup.pl>