switch case was redundant as getopt was already telling the issue:
nfc-read-forum-tag3: option requires an argument -- 'o'
Option -o requires an argument.
This fixes also a problem reported by Coverity about missing break:
CID 1090330 (#1 of 1): Missing break in switch (MISSING_BREAK)
unterminated_case: This case (value 63) is not terminated by a 'break' statement.